Adaptive immune response ranking is associated with reproductive phenotypes in grazing dairy cows divergent in genetic merit for fertility traits

A strong adaptive immune response has been reported to have positive effects on fertility; therefore, we investigated antibody- and cell-mediated adaptive immune responses (AMIR and CMIR, respectively) and their associations with reproductive phenotypes using a population of animals that differed in their estimated genetic merit for fertility traits (fertility breeding value; FertBV). Holstein-Friesian heifers (n = 528) grazed on pasture in 4 herds based on age. These herds included 277 heifers of positive (POS) FertBV and 251 of negative (NEG) FertBV. The adaptive immune response (IR) was evaluated before puberty at 7.5 mo of age and used to rank animals as high, average, or low for AMIR, CMIR, and overall IR (combined CMIR and AMIR). The animals were studied from 12 wk of age through to the end of their second lactation to measure growth, puberty, and timing and success of fertility phenotypes, including those related to ovulation and pregnancy. Initial analysis indicated no difference in fertility outcomes between cows ranked as high or average for AMIR (n = 55, n = 407, respectively), CMIR (n = 87, n = 354, respectively), and IR (n = 29, n = 470, respectively), so these groups were pooled as HiAv-IR. Proportions of heifers of POS FertBV were similar within HiAv and low categories across AMIR (0.52 and 0.58, respectively), CMIR (0.51 and 0.59, respectively), and IR (0.53 and 0.48, respectively). Heifers with HiAv-IR had a greater average daily weight gain from 13 to 52 wk of age (661 g, 95% confidence interval 652, 669 vs. 619 g, 95% confidence interval 591, 647) and tended to be younger at puberty (371 d, 95% confidence interval 366, 377 vs. 385 d, 95% confidence interval 369, 401) than low-IR heifers. Low-CMIR cows of a NEG FertBV had a >40 d longer calving to first ovulation interval during their first lactation compared with HiAv-CMIR NEG FertBV cows. Low-CMIR cows also had decreased pregnancy rates at both 3 wk (25% ± 7% vs. 42% ± 3%; least squares means ± standard error) and 6 wk (33% ± 7% vs. 54% ± 3%; least squares means ± standard error) into the seasonal breeding period during their first lactation, compared with HiAv-CMIR cows. In summary, although the number of POS and NEG FertBV cows was similar in each immune group; interaction effects between FertBV and immune ranking on reproductive phenotypes are evident when cows were ranked by the overall IR. There were also associations between dairy cows' CMIR ranking and ability to return to estrus and become pregnant early in the breeding period, which will have benefits in seasonal breeding systems.     

Association of bovine leukocyte antigen (BoLA) DRB3.2 with immune response, mastitis, and production and type traits in Canadian Holsteins

Data collected from 328 Canadian Holsteins in a research herd at the University of Guelph were used to study associations among expression of bovine leukocyte antigen (BoLA) DRB3.2 alleles, immune response, mastitis resistance via somatic cell counts (SCC), and clinical mastitis, as well as to extend these results to production and type traits. Accordingly, groups of cows were evaluated in vivo for both the antibody-mediated immune response (AMIR) and the cell-mediated immune response (CMIR), which generally predominate in responses to extracellular and intracellular pathogens, respectively. Of note was that associations between BoLA DRB3.2 alleles and immune responses tended to be in the opposite sign for the 2 AMIR and CMIR traits examined. For example, alleles DRB3.2*3 and *24 were associated with higher AMIR but lower CMIR, whereas allele *22 was associated with lower AMIR but higher CMIR. This finding is in agreement with the hypothesis that both traits are genetically independent and represent opposing type 1 and type 2 immune responses. Additionally, BoLA DRB3.2*3 and *11 were associated with lower SCC, whereas alleles *22 and *23 were associated with higher SCC. Finally, allele DRB3.2*3 was also associated with less clinical mastitis, whereas allele *8 was associated with higher mastitis risk. Allele *3 was of particular relevance because it was associated with increased antibodies, as well as reduced mastitis and SCC. This could be due to an indirect relationship between the ability to produce a high antibody response and enhanced defense against intrammamary infections caused by extracellular pathogens. Consequently, the BoLA DRB3.2*3 allele should be investigated further as a candidate for resistance to some types of intramammary infections, the important caveat being its association with lower CMIR, particularly with one of the test antigens used to evaluate delayed-type hypersensitivity. The results of associations between BoLA DRB3.2 and production traits were, in some cases, antagonistic in that BoLA DRB3.2 alleles *11 and *23, which are associated with increased production traits, were associated with lower and higher SCC, respectively. Collectively, these findings advocate the use of alleles *3, *23, and *22 as reference points for more detailed mechanistic studies. This does not imply that genetic selection for mastitis resistance should be based on BoLA alleles, but that information on a variety of genes may aid in identification and selection for improved health.     

Antibody and cell-mediated immune responses and survival between Holstein and Norwegian Red × Holstein Canadian calves

As an extension of a former study, the objectives of this study were to evaluate purebred Holstein (HO; n = 140) and crossbred Norwegian Red × Holstein (NRFX; n = 142) calves for antibody (AMIR) and cell-mediated immune responses (CMIR) as well as survival. Blood was collected on d 0, 14, and 21, and calves were immunized on d 0 and 14 with type 1 (Candida albicans) and type 2 (hen egg white lysozyme) antigens, which have been shown to induce CMIR and AMIR, respectively. Day 21 background skin-fold measurements of either side of the tail-fold were taken and intradermal injections of test (type 1 antigen) and control (phosphate saline buffer) were administered. Day 23 final skin-fold measurements were taken to assess delayed type hypersensitivity as an indicator of CMIR. Survival data were obtained from CanWest Dairy Herd Improvement. Statistical Analysis System general linear models were used to analyze all immune response and survival data and to determine statistical significance between breeds. Results showed that NRFX had greater primary IgM, IgG, IgG1, and secondary IgG1 antibody response, as well as greater primary IgG1:IgG2 ratio to the type 2 antigen compared with HO. The NRFX also had greater primary IgG1 and IgG2, and secondary IgG2 antibody response as well as greater primary IgG1:IgG2 ratio to the type 1 antigen. The NRFX calves had a tendency toward greater survival from age at immune response testing to calving. No difference was observed between breeds for other secondary antibody response traits or delayed type hypersensitivity. Results indicate NRFX have greater AMIR and therefore may have enhanced defense against extracellular pathogens. This may contribute to increased survival compared with HO. Both breeds, however, likely have similar defense against intracellular pathogens, because no differences in CMIR were observed. In general, these results may suggest that crossbreeding could improve resistance to certain diseases in dairy calves, resulting in decreased input costs to producers for crossbred calves compared with purebred calves. However, more research with larger sample sizes and different breeds should be conducted to confirm these results and obtain a complete picture of the benefits of crossbreeding on immune response traits in calves.     

Genetic parameters of adaptive immune response traits in Canadian Holsteins

The objectives of this study were to estimate genetic parameters of cell-mediated (CMIR) and antibody-mediated (AMIR) immune response (IR) traits of Holstein cattle on a national scale and to associate estimated breeding values of CMIR, AMIR, and overall IR with routinely evaluated traits in Canada. In collaboration with the Canadian Bovine Mastitis Research Network, 445 Holstein cows from 42 herds across Canada were immunized to measure delayed-type hypersensitivity as an indicator of CMIR and serum antibody for AMIR to putative type 1 and type 2 test antigens, respectively. Primary (d 14) and secondary (d 21) AMIR were measured for both IgG1 and IgG2. A series of uni- and bivariate linear animal models were used to estimate genetic parameters and breeding values for CMIR and the 4 AMIR traits. The models included the fixed effects of parity and stage of lactation and the random effects of herd-technician, animal, and residual. Heritability of CMIR was 0.19 (SE=0.10) and for AMIR traits ranged from 0.16 to 0.41 (SE=0.09-0.11) depending on time and antibody isotype. The genetic correlations between CMIR and AMIR were negative and ranged from -0.13 to -0.45 (SE=0.32-0.46). The results indicate adaptive immune response traits are moderately heritable and provide a potential for genetic selection. The negative genetic correlations between CMIR and AMIR indicate the importance of considering both traits in breeding for overall disease resistance. Significant beneficial associations between the reproductive traits number of services and first service to conception were found, which may indicate these reproductive traits would improve with genetic selection for enhanced immune response.     

Short communication: Prevalence of digital dermatitis in Canadian dairy cattle classified as high,average, or low antibody- and cell-mediated immune responders

Lameness is a major animal welfare issue affecting Canadian dairy producers, and it can lead to production, reproduction, and health problems in dairy cattle herds. Although several different lesions affect dairy cattle hooves, studies show that digital dermatitis is the most common lesion identified in Canadian dairy herds. It has also been shown that dairy cattle classified as having high immune response (IR) have lower incidence of disease compared with those animals with average and low IR; therefore, it has been hypothesized that IR plays a role in preventing infectious hoof lesions. The objective of this study was to compare the prevalence of digital dermatitis in Canadian dairy cattle that were classified for antibody-mediated (AMIR) and cell-mediated (CMIR) immune response. Cattle (n = 329) from 5 commercial dairy farms in Ontario were evaluated for IR using a patented test protocol that captures both AMIR and CMIR. Individuals were classified as high, average, or low responders based on standardized residuals for AMIR and CMIR. Residuals were calculated using a general linear model that included the effects of herd, parity, stage of lactation, and stage of pregnancy. Hoof health data were collected from 2011 to 2013 by the farm's hoof trimmer using Hoof Supervisor software (KS Dairy Consulting Inc., Dresser, WI). All trim events were included for each animal, and lesions were assessed as a binary trait at each trim event. Hoof health data were analyzed using a mixed model that included the effects of herd, stage of lactation (at trim date), parity (at trim date), IR category (high, average, and low), and the random effect of animal. All data were presented as prevalence within IR category. Results showed that cows with high AMIR had significantly lower prevalence of digital dermatitis than cattle with average and low AMIR. No significant difference in prevalence of digital dermatitis was observed between high, average, and low CMIR cows. These results indicate that having more robust AMIR is associated with lower prevalence of digital dermatitis hoof lesions.     

Associations between immune competence,stress responsiveness,and production in Holstein-Friesian and Holstein-Friesian × Jersey heifers reared in a pasture-based production system in Australia

The objectives of this study were to assess antibody and cellular immune responses in first-lactation dairy heifers reared under a pasture-based production system and to investigate associations between immune competence and stress responsiveness, health, and productivity. A commercial vaccine was used to induce antibody and cellular immune responses and, based on measured responses, animals were classified as above average, average, and below average for each trait independently and in combination (overall immune competence). Overall immune competence phenotypic rankings were generated by combining standardized residual values for antibody and cellular responses measured in individual heifers. Cortisol responses to handling and yarding were used to assess stress responsiveness, worm egg counts were used to assess internal parasite burden, somatic cell counts to assess udder health and estimates of total daily milk volume, and milk fat and milk protein contents to assess productivity. A total of 393 Holstein-Friesian and Holstein-Friesian × Jersey crossbred heifers from 2 herds practicing seasonal calving in a pasture-fed production system were enrolled in the study. The immune competence phenotypes of individual heifers were assessed before their first mating and their subsequent performance during their first lactation was monitored. Animals with below-average antibody and cellular immune competence had higher serum cortisol concentrations compared with their counterparts following handling, suggesting they had a reduced ability to cope with management-induced stress. Furthermore, a significant negative (favorable) correlation was observed between antibody responses and stress responsiveness. Similarly, correlations between antibody responses and internal parasite burden were significant and negative (favorable). No correlations were observed between overall immune competence and milk yield, milk fat, and milk protein content.     

Differences in udder health and immune response traits of Holstein-Friesians, Norwegian Reds, and their crosses in second lactation

The objective of this study was to investigate potential differences in udder health and immune response traits among Holstein-Friesian (HF), Norwegian Red (NR), and NR × HF (NRX) cows on 30 commercial Irish dairy farms. A total of 648 second-lactation cows (HF n = 274, NR n = 207, and NRX n = 167) were immunized with hen egg white lysozyme (HEWL) to induce antibody-mediated immune response (AMIR). Candida albicans was used to induce a cell-mediated immune response, with in vivo delayed-type hypersensitivity used as the indicator. Antibody response to HEWL was measured by ELISA. Udder health defined as mean somatic cell score (SCS) over the lactation, mean SCS within 30 d of the beginning of the immunization, peak SCS for each individual cow during lactation, and incidence of mastitis were statistically superior for the NR. The NR had a greater primary AMIR, producing greater concentrations of anti-HEWL immunoglobulin G on d 14 compared with HF and NRX. No difference was observed among the breed groups in the magnitude of secondary AMIR (d 21 post-immunization) or cell-mediated immune response. The proportion of high and low responders was similar across breed groups. Cows with high AMIR and high cell-mediated immune response had significantly lower mean SCS within 30 d of the start of the immunization, but greater occurrence of clinical mastitis, recorded as a binary trait over the course of the lactation. Otherwise, no significant difference in udder health was evident between cows designated as high and low responders. Although differences in mean breed group SCS values were in line with group mean AMIR values, no association was found among the traits when correlated on an individual cow basis. Results highlight the superiority of the NR with regard to udder health and suggest that improvements to udder health may result from crossbreeding with the NR. However, the immune response traits investigated proved to be inconsistent indicators of udder health.     

Symposium review: Immunological detection of the bovine conceptus during early pregnancy

Infertility and subfertility reduce the economic viability of dairy production. Inflammation reduces conception rates in dairy cattle, but surprisingly little information exists about the populations and the functions of immune cells at the conceptus–maternal interface during the periattachment period in dairy cattle. Early pregnancy is accompanied by immune stimulation at insemination and conceptus secretion of IFN-τ, pregnancy-associated glycoproteins, prostaglandins, and other molecules whose effects on immune function during early pregnancy have not been determined. Our working hypothesis is that pregnancy induces changes in immune cell populations and functions that are biased toward immunological tolerance, tissue remodeling, and angiogenesis. This review summarizes current knowledge, starting with insemination and proceeding through early pregnancy, as this is the period of maximal embryo loss. Results indicated that early pregnancy is accompanied by a marked increase in the proportion of endometrial immune cells expressing markers for natural killer (CD335) cells and cytotoxic T cells (CD8) along with an increase in cells expressing major histocompatibility class II antigens (macrophages and dendritic cells). This is accompanied by increased abundance of mRNA for IL-15, a natural killer growth factor, and IL-10 in the endometrium during early pregnancy. Furthermore, expression of indoleamine 2,3 dioxygenase was 15-fold greater in pregnant compared with cyclic heifers at d 17, but then declined by d 20. This enzyme converts tryptophan to kynurenine, which alters immune function by creating a localized tryptophan deficiency and by activation of the aryl hydrocarbon receptor and induction of downstream tolerogenic mediators. Expression of the aryl hydrocarbon receptor is abundant in the bovine uterus, but its temporal and spatial regulation during early pregnancy have not been characterized. Pregnancy is also associated with increased expression of proteins known to inhibit immune activation, including programed cell death ligand-1 (CD274), lymphocyte activation gene-3 (CD223), and cytotoxic T-lymphocyte associated protein-4 (CD152). These molecules interact with receptors on antigen-presenting cells and induce lymphocyte tolerance. Current results support the hypothesis that early pregnancy signaling in dairy heifers involves changes in the proportions of immune cells in the endometrium as well as induction of molecules known to mediate tolerance. These changes are likely essential for uterine wall remodeling, placentation, and successful pregnancy.     

Short communication: Association of disease incidence and adaptive immune response in Holstein dairy cows

The objective of this study was to use previously calculated estimated breeding values for cell- (CMIR) and antibody-mediated immune responses (AMIR) to determine associations between immune response (IR) and economically important diseases of dairy cattle. In total, 699 Holsteins were classified as high, average, or low for CMIR, AMIR, and overall IR (combined CMIR and AMIR), and associations with mastitis, metritis, ketosis, displaced abomasums, and retained fetal membranes were determined. The incidence of mastitis was higher among average cows as compared with cows classified as high AMIR [odds ratio (OR)=2.5], high CMIR (OR=1.8), or high IR (OR=1.8). Low-CMIR cows had a higher incidence of metritis (OR=11.3) and low-IR cows had a higher incidence of displaced abomasum (OR=4.1) and retained fetal membrane (OR=2.8) than did average responders. Results of this study show that cows classified as high immune responders have lower occurrence of disease, suggesting that breeding cattle for enhanced IR may be a feasible approach to decrease the incidence of infectious and metabolic diseases in the dairy industry.     

Response to kisspeptin and gonadotropin-releasing hormone agonist administration in Holstein-Friesian dairy heifers with positive or negative genetic merit for fertility traits

Previous research has identified that Holstein-Friesian dairy heifers with positive (POS) genetic merit for fertility traits (FertBV) reach puberty earlier than heifers with negative (NEG) FertBV. The hypothalamus-pituitary-gonadal (HPG) axis is functional in heifers before the onset of puberty, with increased LH release evident as heifers progress toward puberty. We investigated the functionality of the HPG axis in peripubertal Holstein-Friesian dairy heifers with divergent POS or NEG FertBV, hypothesizing that the earlier puberty onset of POS heifers is associated with earlier activation of the HPG axis than in NEG heifers. In experiment 1, we tested the dose responsiveness of POS heifers to an intravenous injection of either kisspeptin [Kiss; 2, 4, or 8 µg/kg of body weight (BW); n = 3 per dose] or a GnRH agonist (buserelin; 5, 10, or 20 ng/kg of BW; n = 3 per dose). The use of these 2 agonists investigates the status of the HPG axis in both the hypothalamus (Kiss) and pituitary (buserelin) glands. Doses of 4 µg/kg BW of Kiss and 10 ng/kg BW of buserelin produced submaximal LH responses and were used in experiment 2, in which previously unused POS (n = 22) and NEG (n = 18) FertBV heifers were challenged with both agonists at 10 and 12 mo of age in a partial crossover design. Heifers were randomly allocated to treatment groups, balanced for age and BW. The LH response to buserelin was greater in POS heifers than NEG heifers at 10 mo of age, with no difference in response at 12 mo. The FSH response to buserelin and the LH and FSH responses to Kiss did not differ between the POS and NEG heifers at either age. These results indicate an association between divergent genetic merit for fertility and the LH release to buserelin at 10 mo of age, supporting the hypothesis that gonadotropin responsiveness to a GnRH agonist is more advanced in POS heifers than in NEG heifers.     

Heifers with positive genetic merit for fertility traits reach puberty earlier and have a greater pregnancy rate than heifers with negative genetic merit for fertility traits

This study investigated the hypothesis that dairy heifers divergent in genetic merit for fertility traits differ in the age of puberty and reproductive performance. New Zealand's fertility breeding value (FertBV) is the proportion of a sire's daughters expected to calve in the first 42 d of the seasonal calving period. We used the New Zealand national dairy database to identify and select Holstein-Friesian dams with either positive (POS, +5 FertBV, n = 1,334) or negative FertBV (NEG, ?5% FertBV, n = 1,662) for insemination with semen from POS or NEG FertBV sires, respectively. The resulting POS and NEG heifers were predicted to have a difference in average FertBV of 10 percentage points. We enrolled 640 heifer calves (POS, n = 324; NEG, n = 316) at 9 d ± 5.4 d (± standard deviation; SD) for the POS calves and 8 d ± 4.4 d old for the NEG calves. Of these, 275 POS and 248 NEG heifers were DNA parent verified and retained for further study. The average FertBV was +5.0% (SD = 0.74) and ?5.1% (SD = 1.36) for POS and NEG groups, respectively. Heifers were reared at 2 successive facilities as follows: (1) calf rearing (enrollment to ～13 wk of age) and (2) grazier, after 13 wk until 22 mo of age. All heifers wore a collar with an activity sensor to monitor estrus events starting at 8 mo of age, and we collected weekly blood samples when individual heifers reached 190 kg of body weight (BW) to measure plasma progesterone concentrations. Puberty was characterized by plasma progesterone concentrations >1 ng/mL in at least 2 of 3 successive weeks. Date of puberty was defined when the first of these samples was >1 ng/mL. Heifers were seasonally bred for 98 d starting at ～14 mo of age. Transrectal ultrasound was used to confirm pregnancy and combined with activity data to estimate breeding and pregnancy dates. We measured BW every 2 wk, and body condition and stature at 6, 9, 12, and 15 mo of age. The significant FertBV by day interaction for BW was such that the NEG heifers had increasingly greater BW with age. This difference was mirrored with the significant FertBV by month interaction for average daily gain, with the NEG heifers having a greater average daily gain between 9 and 18 mo of age. There was no difference in heifer stature between the POS and NEG heifers. The POS heifers were younger and lighter at puberty, and were at a lesser mature BW, compared with the NEG heifers. As a result, 94 ± 1.6% of the POS and 82 ± 3.2% of the NEG heifers had reached puberty at the start of breeding. The POS heifers were 20% and 11% more likely to be pregnant after 21 d and 42 d of breeding than NEG heifers (relative risk = 1.20, 95% confidence interval of 1.03–1.34; relative risk = 1.11, 95% confidence interval of 1.01–1.16). Results from this experiment support an association between extremes in genetic merit for fertility base on cow traits and heifer reproduction. Our results indicate that heifer puberty and pregnancy rates are affected by genetic merit for fertility traits, and these may be useful phenotypes for genetic selection.     

The association of immune response and colostral immunoglobulin G in Canadian and US Holstein-Friesian dairy cows

In cattle, maternal immunoglobulins are transferred through colostrum to provide passive immunity to the neonatal calf once they are absorbed into circulation. Cows can be assessed for antibody- and cell-mediated immune responses (AMIR and CMIR, respectively), and through estimated breeding values (EBV) and genomic parent averages (GPA), cows can be classified as having high, average, or low immune response (IR). The objective of this study was to identify associations of colostral IgG concentrations with IR in dairy cows. High IR dairy cows identified by GPA or EBV were hypothesized to produce higher colostral IgG concentrations than cows with average or low IR. Colostrum was collected from Holstein dairy cows from 3 large commercial herds (n = 590) in the United States and 1 research herd at the Ontario Dairy Research Centre (n = 275) in Canada. For the US herds, IR GPA were available through genotyping. For the Canadian herd, IR EBV were available through phenotyping and pedigree information. Colostral IgG concentrations were measured by radial immunodiffusion and analyzed using general linear models in SAS. Based on a prediction equation, cows in US herds with a CMIR GPA of 1 would have colostral IgG concentrations 6.3 g/L higher on average than cows with a CMIR GPA of 0. High CMIR cows produced statistically greater colostral IgG concentrations (least squares mean ± standard error of the mean, 107.5 ± 7.7 g/L) than low CMIR cows (91.4 ± 7.1 g/L), with intermediate values for average CMIR cows (105.1 ± 5.6 g/L). No differences were found among AMIR categories in US cows. The Canadian herd showed a trend for cows with high CMIR EBV (continuous variable) to produce greater colostral IgG. No differences were observed among high, average, and low AMIR EBV classifications in Canadian cows. The findings suggest that selective breeding of Holstein cows to enhance CMIR could contribute to higher-quality colostrum in succeeding generations.     

Effect of dietary ascorbyl-2-phosphate on immune function after transport to a feeding facility

Effects of dietary ascorbyl-2-phosphate on immune function after a 210-km trip were measured in 18 Holstein heifers. After transport on d 0, 10 g of ascorbyl-2-phosphate each were added to the diets of 10 heifers, whereas eight heifers were fed a control diet. Plasma cortisol concentrations increased by an average of 25.6 microgram/ml on d 0 following transport, but by d 7 after transport had decreased to pretransport levels. Average daily gain was lower in heifers fed ascorbyl-2-phosphate from d 28 to 49 d after transport, but did not differ over the entire study. Feeding ascorbyl-2-phosphate maintained plasma ascorbate concentrations on d 7 post-transport, which decreased in control heifers. Plasma keyhole limpet hemocyanin antibody titers were significantly higher in control heifers from d 7 to 49. Mononuclear leukocyte proliferation responses were decreased on d 0 in lymphocytes stimulated by mitogens, with pokeweed mitogen-stimulated cells showing less of a response than cells stimulated by the other mitogens. In the absence of mitogens, dietary ascorbyl-2-phosphate increased basal 3H-methyl thymidine incorporation by cultured lymphocytes. Across diets and mitogens, lymphocytes treated with cortisol showed decreased 3H-methyl thymidine incorporation. Transportation acted as a stressor, as evidenced by the increased plasma cortisol levels at d 0 immediately after transport, but immunological effects were not apparent by d 7. Feeding ascorbyl-2-phosphate maintained plasma ascorbate concentrations on d 7, but had negative effects on immune responses posttransport.     

Response of growing Japanese quails to dietary concentration of L‐threonine

The influence of dietary levels of L ‐threonine (Thr) on growth and immune response was investigated in growing (0–5 weeks of age) Japanese quails (n = 288). Three dietary treatments were formulated using three levels of Thr [9.6, 10.2 and 11.2 kg^?1 diet dry matter (DM)] at a fixed protein level of 233 g kg^?1 and an energy level of 12.15 MJ (2900 kcal) metabolizable energy (ME) kg^?1 feed dry matter. A metabolism trial with a 3‐day collection period was conducted at the third week of age employing all the birds. The cell‐mediated (using PHA‐P) and humoral (SRBC response) immune responses were measured at the fourth week of age. Carcass traits were assessed at the end of fifth week of age. Body weight gain was lower (P < 0.01) in birds received 9.6 g Thr kg^?1 DM than in groups fed 10.2 g or 11.2 g kg^?1 DM in the diet, but there was no significant difference in gain between the groups fed 10.2 or 11.2 g Thr kg^?1 DM in the diet. Feed intake differed significantly owing to Thr levels being lowest (P < 0.05) at 9.6 g Thr kg^?1 DM in the diet. Feed conversion ratio (FCR), protein efficiency and energy efficiency improved at the 11.2 g kg^?1 level from 0 to 3 weeks of age; however, from 3 to 5 weeks of age, better FCR emanated from a diet with 9.6 g Thr kg^?1 DM. The nitrogen balance did not differ (P > 0.05) with Thr level. Carcass traits, relative weight of immune organs and cell‐mediated (PHA‐P) and humoral (SRBC response) immune responses did not differ significantly (P > 0.05) as a result of the dietary treatments. Copyright © 2006 Society of Chemical Industry     

Evaluation of attenuated, live staphylococcal mastitis vaccine in lactating heifers

Four heifers were immunized in late pregnancy with two doses of attenuated, live Staphylococcus aureus and challenged during early lactation by intramammary infusion into one quarter of approximately 100 organisms of the same attenuated strain. Three unvaccinated control heifers were challenged similarly. At challenge immunoglobulins G1 and G2 antibodies against Staphylococcus aureus surface antigens were significantly greater in blood serum of vaccinated heifers than in controls. Also at challenge, serum from vaccinated heifers had a significantly greater opsonizing capacity for Staphylococcus aureus than did that of controls. The challenge dose of Staphylococcus aureus did not produce prolonged clinical signs of acute mastitis in any of the heifers; however, once of the control animals remained chronically infected. There was a decrease of milk production following challenge for controls but no such decrease for the immunized heifers. Taken together, results of clinical assessments, bacteriology, and measurements of milk production suggested that vaccinated heifers had higher resistance to the challenge dose than did controls.     

Genomic merit for reproductive traits. I: Estrous characteristics and fertility in Holstein heifers

Genetic selection of dairy cattle in the United States has included reproductive traits (daughter pregnancy rate, DPR; heifer conception rate, HCR), which is believed to have partly contributed to halting the decline in reproductive performance. The objectives of the current study were to evaluate the association among genomic merit for DPR (GDPR) and HCR (GHCR) with estrous characteristics measured by an automated device. Holstein heifers (n = 1,005) were genotyped at 2 mo of age and were classified into quartiles (Q1 = lowest, Q4 = highest) according to the GDPR and GHCR values of the study population. At 10 to 11 mo of age, heifers were fitted with a collar that recorded activity and rumination and determined the occurrence of estrus according to changes in activity and rumination compared with the individual's baseline values. Estrous characteristics of spontaneous estruses (SPE) and PGF_2α-synchronized estruses (PGSE) were recorded. Heifers had their estrous cycle synchronized with PGF_2α and following detection of estrus received either artificial insemination or embryo transfer according to the herd's genetic selection program. Heifers in Q2 (17.7 ± 0.3 h) of GHCR tended to have longer SPE than heifers in Q4 (16.7 ± 0.3 h). The interaction between GDPR and GHCR was associated with the likelihood of activity peak (0 = no estrus, 100 = maximum activity) ≥80 at SPE because, among heifers in Q3 and Q4 of GHCR, those in Q1 of GDPR were less likely to have an activity peak ≥80. Heifers in Q1 and Q2 of GDPR had reduced hazard of estrus within 7 d of the first PGF_2α treatment compared with heifers in Q4 of GDPR. Heifers in Q1 (16.1 ± 0.4 h) of GDPR had shorter PGSE than heifers in Q2 (17.6 ± 0.4 h) and Q4 (17.4 ± 0.4 h) and tended to have shorter PGSE than heifers in Q3 (17.4 ± 0.4 h). Rumination nadir on the day of PGSE was greater for heifers in Q1 (?30.1 ± 0.9 min/d) of GDPR compared with heifers in Q4 (?33.7 ± 0.9 min/d). Among heifers receiving only artificial insemination, those in Q1 of GHCR (adjusted hazard ratio = 0.65; 95% confidence interval = 0.48–0.88) became pregnant at a slower rate than heifers in Q4. Genomic merit for HCR was negatively associated with SPE but tended to be positively associated with hazard of pregnancy, whereas GDPR was positively associated with PGSE and hazard of estrus. Selection of dairy cattle for DPR and HCR may improve reproductive performance through different pathways, namely estrous characteristics and pregnancy establishment.     

Immune response after an experimental intramammary challenge with killed Staphylococcus aureus in cows and heifers vaccinated and not vaccinated with Startvac,a polyvalent mastitis vaccine

An experimental trial was conducted to explore the effect of vaccination with a polyvalent vaccine against mastitis (Startvac) on the early immune response after experimental intramammary challenge with a heterologous killed Staphylococcus aureus strain. The effect of vaccination on milk production, clinical signs, quarter milk somatic cell count, milk polymorphonuclear neutrophilic leukocyte (PMN) concentration and viability, the concentration of antigen-specific antibodies [slime associated antigenic complex (SAAC) and J5] and their IgG1 and IgG2 subtypes in both serum and whey, and the antigen-specific IFN-γ, IL-4, and IL-17 production by blood lymphocytes after in vitro stimulation with S. aureus and Escherichia coli extracts were determined. A cohort of 8 clinically healthy end-term cows and heifers were conveniently selected, of which half was vaccinated with Startvac at 45 and 10 d before the expected calving date and half served as nonvaccinated control animals. At 15 d in milk, 2 contralateral quarters of each of the 8 animals were challenged with 2 × 10⁹ cfu/mL of the formaldehyde-killed S. aureusC195strain. The 2 other quarters were infused with phosphate-buffered saline and served as control quarters. The increase in both quarter milk somatic cell count and PMN concentration and the drop in milk production after S. aureus inoculation was less pronounced in the vaccinates than in the nonvaccinates, reflecting a less severe inflammatory response. No significant differences in PMN viability between vaccinates and nonvaccinates could be demonstrated. The serum SAAC- and J5-specific antibody concentration significantly increased across the dry period in the vaccinated animals only. The whey concentration of SAAC-specific antibodies was significantly higher in vaccinates than in nonvaccinates at both 15 and 17 d in milk, independent from the challenge status of the quarters. No significant differences in the whey J5-specific antibody concentration were observed. Vaccination with Startvac seems to primarily evoke a Th2 response for S. aureus characterized by a shift toward the IgG1 antibody subtype and accompanied by a less pronounced Th1 response. The type of response against E. coli was less clear, though a weak but significant shift toward the IgG2 antibody subtype after vaccination and high IFN-γ levels after in vitro stimulation suggest a Th1 response. The increased SAAC-specific antibody concentration in whey in vaccinates compared with nonvaccinates most probably triggers the opsonization of the inoculated S. aureus bacteria, resulting in a more efficient elimination of the bacteria from the mammary gland.     

Genetic parameters and responses of linear type,yield traits,and somatic cell scores to divergent selection for predicted transmitting ability for type in Holsteins

The objective was to examine the direct and correlated responses of linear type, yield traits, and somatic cell scores (SCS) to divergent selection for predicted transmitting ability for type (PTAT) in Holsteins, while maintaining selection for yield traits across lines. For four generations, one-half of the University of Nebraska research Holstein herd was bred to Holstein sires with PTAT > 1.50 and the other half to sires with PTAT < 1.25, with nearly equal predicted transmitting abilities for yield traits for both groups. Estimates of genetic and residual correlations and heritabilities were obtained from REML estimates of (co)variance components. Model for type traits included fixed effect of date cows were classified, effects of age in days at freshening, and stage of lactation at classification. Year-season when cows freshened was fixed effect in model for yield and SCS. Animal genetic and residual effects were random. Final score, milk, fat, and protein yields, and SCS had heritability estimates of 0.38, 0.13,0.22, 0.09, and 0.38, respectively. Heritability estimates for type traits ranged from 0.04 to 0.52. Estimates of genetic correlations of final score with SCS and milk, fat, and protein yields were -0.64, 0.01, -0.18, and 0.06, respectively. Estimates of genetic correlations among linear type traits ranged from -0.77 to 1.00. Means of estimated breeding values for final score, stature, strength, body depth, fore udder attachment, rear udder height and width, udder cleft, udder depth, and front teat placement were significantly different between lines in the third generation. Milk, fat, and protein yields were not significantly different between lines in third generation, whereas SCS was significantly different. Estimate of genetic correlation between final score and SCS suggest that selection on PTAT would result in a change for SCS. In this study, divergent selection on PTAT of sires had a significant effect on udder and body traits, but little or no effect on feet and leg traits.     

Assessment of a commercially available early conception factor (ECF) test for determining pregnancy status of dairy cattle

The Early Conception Factor (ECF) test is a commercially available qualitative assay that reportedly detects a pregnancy-associated glycoprotein present in bovine serum within 48 h after conception. One concern with previous assessments of this test is that animals with viable embryos early during pregnancy that subsequently undergo embryonic loss before pregnancy diagnosis increase the rate of false-positive results and bias the assessment. To preclude this possibility, noninseminated Holstein cows (n = 9) and heifers (n = 8) were evaluated as an unequivocal source of nonpregnant animals, and Holstein cows (n = 17) and heifers (n = 1) inseminated at estrus and in which at least one embryo of transferable quality was recovered at a nonsurgical flush 6 d after artificial insemination were evaluated as an unequivocal source of pregnant animals. Blood samples were collected from all animals 6 d after estrus, which was immediately before embryo collection in pregnant animals. Each serum sample was evaluated using two ECF test cassettes (tests 1 and 2), and the result of each test cassette was interpreted by two independent readers (readers 1 and 2). Test sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 86, 4, 49, 23, and 46%, respectively. Although the observed agreement between readers (91% for test 1; 89% for test 2) and between tests for the same serum sample (94% for reader 1; 91% for reader 2) was high, the overall rates of false-positive and false-negative ECF test results were 96 and 14%, respectively. We conclude that the ECF test is an unreliable method for determining pregnancy status of dairy cattle on day 6 after estrus.     

Association of lipid-related genes implicated in conceptus elongation with female fertility traits in dairy cattle

Elongation of the preimplantation conceptus is a requirement for pregnancy success in ruminants, and failures in this process are highly associated with subfertility in dairy cattle. Identifying genetic markers that are related to early conceptus development and survival and utilizing these markers in selective breeding can improve the reproductive efficiency of dairy herds. Here, we evaluated the association of 1,679 SNP markers within or close to 183 candidate genes involved in lipid metabolism of the elongating conceptus with different fertility traits in US Holstein cattle. A total of 27,371 bulls with predicted transmitting ability records for daughter pregnancy rate, cow conception rate, and heifer conception rate were used as the discovery population. The associations found in the discovery population were validated using 2 female populations (1,122 heifers and 2,138 lactating cows) each with 4 fertility traits, including success to first insemination, number of services per conception, age at first conception for heifers, or days open for cows. Marker effects were estimated using a linear mixed model with SNP genotype as a linear covariate and a random polygenic effect. After multiple testing correction, 39 SNP flagging 27 candidate genes were associated with at least one fertility trait in the discovery population. Of these 39 markers, 3 SNP were validated in the heifer population and 4 SNP were validated in the cow population. The 3 SNP validated in heifers are located within or near genes CAT, MYOF, and RBP4, and the 4 SNP validated in lactating cows are located within or close to genes CHKA, GNAI1, and HMOX2. These validated genes seem to be relevant for reducing pregnancy losses, and the SNP within these genes are excellent candidates for inclusion in genomic tests to improve reproductive performance in dairy cattle.