Effects of prepartum milking on postpartum reproduction, udder health and production performance in first-calf dairy heifers

Postpartum production performance of dairy heifers may be enhanced by prepartum milking by alleviating the stress of the periparturient period. The objective of this study was to determine the impact of prepartum milking of dairy heifers on postpartum reproduction, udder health, milk production and other associated production characteristics. Pregnant heifers (Holstein, n=21; Jersey n=10) were assigned to either a prepartum milked (premilked, n=15) or control (n=16) group. Premilked heifers were milked twice daily starting 3 weeks prior to anticipated calving dates, and milk yield recorded at each milking. All heifers were evaluated on days 21, 14 and 7 before calving, and udder oedema scores and milk conductivity readings were recorded. Following calving, measurements were taken twice weekly to assess udder oedema, milk conductivity (indicative of udder infection), and reproductive health, which included palpation for uterine tone and uterine position, vaginal electrical impedance (VEI) and the quantification of cross-sectional area of the uterine horns (uterine difference) by transrectal ultrasonography. Uterine tone, uterine position, uterine difference, and VEI did not differ (P>0.10) with treatment. Overall, up to week six inclusive, postpartum premilked heifers had lower (P<0.01) udder oedema scores than control heifers and up to week five inclusive, had lower (P<0.01) milk conductivity readings (indicative of fewer incidences of udder infections) than control heifers. The premilked heifers of both breeds produced more milk (P<0.01) at calving and more milk overall from calving to day 60 postpartum than the control heifers. In summary, udder health and milk production were improved post calving in premilked heifers compared with controls. However, no overt differences in reproductive characteristics were observed between the premilked and control heifers.     

Induced endometritis in early lactation compromises production and reproduction in dairy cows

Objectives of this experiment were to study the effect of infusing utero-pathogenic bacteria to induce endometrial inflammation on productive performance in early lactation and subsequent reproduction. Although endometritis is associated with perturbed reproduction, numerous factors may contribute to the observed association. It was hypothesized that induced endometrial inflammation, resulting in localized and systemic inflammatory responses, compromises production and reproduction. Holstein cows without clinical disease and with less than 18% polymorphonuclear leukocytes (PMN) in endometrial cytology on d 31 ± 3 postpartum had their estrous cycle synchronized. Cows were blocked by parity and genomic breeding value for cow conception rate and, within block, assigned randomly to remain as untreated controls (CON; n = 37) or to receive an intrauterine infusion of 5.19 × 10⁸ cfu Escherichia coli and 4.34 × 10⁸ cfu Trueperella pyogenes during the luteal phase to induce endometrial inflammation (INF; n = 48). Endometrial cytology was taken on d 2 and 7 after treatment to evaluate the proportion of PMN. Rectal temperature, dry matter intake, and yields of milk and components were measured in the first 7 d after treatment. Blood serum was analyzed for concentration of haptoglobin. Leukocytes were isolated from blood on d 2 and 7 after treatment and on d 19 after artificial insemination (AI) and mRNA was quantified for a select group of genes. Cows received AI and reproduction was followed for 300 d postpartum. Bacterial infusion induced endometrial inflammation with increased proportions of PMN in the endometrial cytology on d 2 (4.4 ± 0.7 vs. 26.3 ± 2.8%) and 7 (10.9 ± 1.7 vs. 17.4 ± 2.1%) after treatment, resulting in increased mean prevalence of subclinical endometritis (>10% PMN; 23.3 ± 6.3 vs. 80.9 ± 5.1%). Rectal temperature did not differ between CON and INF, but the concentration of haptoglobin in serum tended to increase in INF compared with CON (113 ± 14 vs. 150 ± 16 µg/mL). Induced endometrial inflammation reduced yields of milk (44.9 ± 0.8 vs. 41.6 ± 0.8 kg/d), protein (1.19 ± 0.03 vs. 1.12 ± 0.03 kg/d), and lactose (2.17 ± 0.04 vs. 2.03 ± 0.04 kg/d) and tended to reduce dry matter intake (20.7 ± 0.5 vs. 19.4 ± 0.6 kg/d) in the first 7 d after treatment. Indeed, the reduction in milk yield lasted 4 wk. However, treatment did not affect yields of energy-corrected milk or fat because treatment with INF increased the concentration of fat in milk (3.54 ± 0.10 vs. 3.84 ± 0.10%). Induced endometrial inflammation reduced pregnancy per AI at all inseminations (33.4 ± 5.1 vs. 21.6 ± 3.7%) and the hazard of pregnancy (0.61; 95% CI = 0.36–1.04), which extended the median days open by 24 d. Blood leukocytes from INF cows had increased mRNA expression of the pro-inflammatory gene IL1B on d 2 and 7 after treatment, but reduced expression of the IFN-stimulated genes ISG15 and MX2 on d 19 after AI. Induced endometrial inflammation depressed production and caused long-term negative effects on reproduction in lactating dairy cows.     

Management practices and heifer characteristics associated with early lactation somatic cell count of Belgian dairy heifers

Associations between somatic cell counts (SCC) from heifers between 5 and 14 d in milk (DIM) and both herd-management practices and heifer characteristics were studied for 1912 heifers in 159 dairy herds in Flanders (Belgium). In higher-producing herds and in herds with an average calving age of heifers > 27 mo, SCC of heifers was lower than in less-producing herds or in herds with an average calving age < or = 27 mo. Heifers raised in herds with a higher bulk-milk somatic cell count had higher SCC. In herds in which heifers calved on slatted floors, heifers had lower SCC compared with herds in which heifers calved on nonslatted floors. A significant difference in SCC was observed between provinces. At the heifer level, SCC decreased with increasing DIM. On average, heifers calving in April to June had higher SCC, compared with those calving in the other months of the year. In the multilevel regression models, nearly all the variations of SCC resided at the heifer level, indicating that preventive measures against udder health problems in freshening dairy heifers should, in the short term, focus more on factors that vary between heifers than on factors that vary between herds. However, for the long term, the need to identify new, and to implement known, herd-level strategies is important.     

Effects of late gestation heat stress on postpartum milk production and reproduction in dairy cattle.

Carry-over effects of late gestation heat stress on postpartum productive and reproductive traits were estimated from DHI records using 341 lactations from six sites in Mississippi. Climatological data were gathered from records of weather stations near the sites. Using multiple linear regression analyses, predictor variables for lactations were age at calving, lactation number, maximum degree-days (above 32.2 degrees C) during the periods 30 and 60 d prepartum, and precipitation 30 and 60 d prepartum. Months and sites were indicator variables. Dependent variables included milk and fat production during early, mid, and late lactation; days to peak lactation; days open; services per conception; and body weight. Age at calving affected milk and fat production in mid and late lactation and services per conception. Degree-days for 60 d prepartum had the greatest negative influence on production variables; its statistical significance was shown in predictions of milk and fat production in early and midlactation. Days open were higher for July than for cows calving in August or September. Sites had effects on many milk and fat measurements and some reproductive traits. These results indicate that heat stress in the last 60 d of gestation has negative effects on some production variables.     

Differences in splanchnic metabolism between late gestation and early lactation dairy cows

In the transition from the pre- to postcalving state, the demands on the cow increase from support of gestation to high rates of milk production. This extra demand is met partly by increased intake but may also involve altered metabolism of major nutrients. Six multiparous Holstein cows were used to monitor changes in net fluxes of nutrients across the portal-drained viscera and liver (splanchnic tissues) between late gestation and early lactation. Blood samples were obtained simultaneously from the portal, hepatic, and subcutaneous abdominal veins and the caudal aorta 18 d before expected calving and 21 or 42 d after calving. On the day of blood sampling and the 3 d preceding sampling, cows were fed every 2 h. The precalving (1.63 Mcal of net energy for lactation/kg and 1,326 g of metabolizable protein/d) and postcalving (1.72 Mcal of net energy for lactation/kg and 2,136 g of metabolizable protein/d) diets were based on corn silage, alfalfa hay, and corn grain. Dry matter intake increased postcalving. Net splanchnic release of glucose increased postpartum because of tendencies for both increased portal absorption and net liver release. Increased removal of lactate, rather than AA, contributed to the additional hepatic gluconeogenesis. Although portal absorption of AA increased with intake at the onset of lactation, hepatic removal of total AA-N tended to decline. This clearly indicates that liver removal of AA is not linked to portal absorption. Furthermore, net liver removal relative to total liver inflow even decreased for Gly, His, Met, Phe, and Tyr. Together, these data indicate that in early lactation, metabolic priority is given to direct AA toward milk protein production rather than gluconeogenesis, in cows fed a corn-based ration.     

Improving energy supply to late gestation and early postpartum dairy cows.

Sixty-five multiparous Holstein cows were used to test the effects of feeding diets of varied ruminal carbohydrate availability during the transition period on dry matter intake, blood metabolites, and lactational performance. Cows received total mixed rations containing either cracked corn or steam-flaked corn beginning 28 d prior to expected calving date. At parturition, cows were assigned to a postpartum total mixed ration that contained either cracked corn or steam-flacked corn. Diets were fed until 63 d in milk. No treatment effects on prepartum or postpartum dry matter intake, body weight, and body condition score were observed. Cows fed steam-flaked corn had lower blood urea N concentrations during the prepartum period and lower plasma nonesterified fatty acid concentrations during the prepartum and postpartum periods. Cows fed steam-flaked corn postpartum produced 2.3 kg/d more milk than cows fed cracked corn during the first 63 d in milk. Fat corrected milk showed no treatment effect. Seven cows were used to evaluate treatment effects on ruminal fermentation and digesta kinetics. Prepartum and postpartum treatments had minimal effects on ruminal fermentation. Feeding steam-flaked corn prepartum decreased apparent fiber digestibility and ruminal NH3 N. Feeding steam-flaked corn postpartum decreased the acetate to propionate ratio. Prepartum and postpartum treatments did not affect digesta kinetics. An increase in ruminal carbohydrate availability during the postpartum period enhanced milk production, but had variable results on ruminal fermentation.     

Timing of insemination in dairy heifers.

Data representing 676 AI of 372 virgin dairy heifers during 1984 to 1987 at the University of Illinois were analyzed by analysis of variance to determine the effect of timing of AI on conception rate. Standing to be mounted, bawling, and attempting to mount were the three criteria used for determining the presence of estrus. More than 90% of the observations were conducted by one herdsperson between 0700 and 1600 h daily. Heifers were artificially inseminated with frozen semen from 58 bulls by one of two technicians. Conception rate on first AI was 56%, determined by return to estrus or 33- to 50-d rectal palpation for pregnancy. Conception rate to second and later AI was near 40%. Eighty-six percent of the heifers conceived during the trial. The average interval between first observation of standing estrus and AI was 10.5 h; the range was 15 min to 33 h. The model discussed contained six variables: time interval between first observation of standing estrus and AI (group), breed, sire within breed, year bred, season bred, and inseminator. The analysis of variance of conception to first AI showed timing of AI and service sire as the two most significant effects. Conception to first AI was worst when AI occurred 13.5 to 33 h after first observation of estrus. No factors considered were significant sources of variation for second or later AI.     

Mortality in Swedish dairy calves and replacement heifers

The mortality of 8,964 heifer calves born in 122 dairy herds in southwest Sweden in 1998 to 2000 was monitored from January 1998 until December 2000. Farmers were requested to send carcasses for necropsy from animals that died from 1 d of age to first calving. Age and seasonal patterns of mortality were investigated using Kaplan-Meier curves. The median herd-level mortality risk was 2.1%. In total, 3.1% of the animals died before 90 d of age, 0.9% between d 91 and 210, and 2.2% between d 211 and first calving or d 810 (27 mo of age). The median age at death was 50 d and the risk of dying was highest during the first week of life. Of the 421 dead animals, 236 (56%) were subjected to either postmortem examination or were diagnosed as having died from trauma based on information from the farmers. In total, pneumonia was the most common cause of death (27%). However, in calves less than 31 d old, enteritis was the most common cause of death; in young stock 211 to 450 d old, trauma dominated; and in young stock more than 450 d old, trauma and calving-related diseases accounted for a majority of the mortality. The largest proportion of deaths was observed from January to March, and in June. Kaplan-Meier curves suggested that housing in small-group pens was associated with the lowest mortality (other housing systems were single pens and large-group pens with automatic milk feeders), but the association was not significant.     

Association between somatic cell count in early lactation and culling of dairy heifers using cox frailty models

The association between somatic cell count (SCC) of dairy heifers in early lactation [SCCel; measured between 5 and 14 d in milk (DIM)] and the culling hazard during the first lactation was studied using Cox frailty models. Udder health problems were the culling reason for 10% of the culled heifers in this study. For each unit increase in the log-transformed SCCel (LnSCCel), the culling hazard increased by 11% [Hazard ratio (HR) = 1.11]. The strength of the association depended on 5 factors. Firstly, the association was stronger when SCCel was recorded after 10 DIM than at an earlier DIM. Secondly, the association was stronger if only culling events for udder disorders were considered (HR = 1.32) instead of all culling events (HR = 1.11). Furthermore, for each unit increase of test-day LnSCC after 14 DIM, modeled as a time-varying covariate, the culling hazard in the first lactation increased by 26% (HR = 1.26). Including LnSCC in the model already containing LnSCCel, reduced the estimate of LnSCCel slightly. Fourth, a higher test-day milk yield, modeled as a time-varying covariate, protected against culling and reduced the magnitude of the effect of LnSCCel as well when taken into account. Finally, the association between LnSCCel and culling was still present, although smaller, in the group of heifers with a second test-day SCC 相似文献   

Utilization of chopped and long alfalfa by dairy heifers

Two physical forms of alfalfa hay, chopped and long, were fed at maintenance and for ad libitum consumption to dairy heifers to determine effects upon digestibility and energy utilization. Ad libitum intake was associated with lower digestibility of dry matter (56 versus 58%), neutral detergent fiber (45 versus 58%), and acid detergent fiber (45 versus 52%). Energy balance was 1.77 Mcal/day at ad libitum versus .08 Mcal/day at maintenance. Dry matter intake was similar for chopped (5.4 kg/day) versus long alfalfa (5.5 kg/day). Digestibilities of dry matter, neutral detergent fiber, acid detergent fiber, and cellulose were 7 to 10 percentage units lower when heifers were fed the chopped alfalfa. Metabolizable energy intake generally reflected digestible energy intake, which was about 2 Mcal/day less for heifers consuming chopped alfalfa. Heat production was similar for the two physical forms. Consequently, heifers consuming chopped alfalfa had lower energy balance. Reducing particle size of the alfalfa resulted in lower dry matter and energy digestibility, presumably because of increased rate of passage. Increased intake to compensate for depressed energy utilization of the chopped alfalfa did not occur; effects upon animal gain could not be assessed.     

Stationary brush use in naive dairy heifers

Weaned dairy heifers are often housed in environments with few appropriate outlets for grooming or oral manipulation. Our objective was to characterize brush use by naive heifers, including patterns over time. In phase 1, groups of 4 heifers (n = 13 groups, 146.4 ± 9.1 d old, mean ± standard deviation; SD) were introduced to a bedded pack pen with 4 wall-mounted brushes (25.4 × 6.0 cm with 3.8-cm-long bristles). On d 1, 2, and 6 of exposure, continuous video recordings were used to observe 2 focal heifers per group for brush use (oral manipulation, grooming, and the sum of total brush use; all averaged at the group level). Latency to use a brush upon entering the pen was 3.4 ± 4.9 min (mean ± SD; range: 0.1 to 17.8 min among individuals). Heifers used the brushes for oral manipulation (39.7 ± 17.5% of brush use, mean ± SD) and grooming (60.3 ± 17.5%), primarily of their heads (89.9 ± 5.4% of grooming). In phase 2, heifers were moved in pairs (n = 13 pairs/treatment) to freestall pens either with (brush treatment) or without (control) brushes mounted inside the stalls for the first 5 d of phase 2 (d 8–12 of the study); on the last day (d 13 of the study), brushes were provided in both treatments. On d 8 (brush treatment) and 13 (both treatments), one focal heifer/pen was recorded for the same behaviors as in phase 1. Linear mixed models were used to evaluate brush use patterns across days (phase 1: d 1, 2, and 6; phase 2 brush treatment: d 8 vs. 13) and between treatments on d 13. In phase 1, brush use was greatest on d 1 [45.9 min; 95% confidence interval (CI): 33.2–63.3 min, back-transformed from natural-log values], decreased on d 2 (25.0 min, 95% CI: 18.4–34.0 min), but then remained steady until d 6 (21.0 min, 95% CI: 15.4–28.5 min); the initial reduction in total brush use was due to changes in grooming, but oral manipulation remained relatively static. In phase 2, heifers in the brush treatment showed similar usage on d 8 versus d 13 (3.8 vs. 3.7 min, 95% CI: 1.9–6.8 vs. 1.9–6.5 min). Compared with heifers with continuous brush access on d 8–12, those in the control treatment showed more brush use on d 13, both for oral manipulation (6.6 vs. 2.5 min, 95% CI: 3.8–11.1 vs. 1.3–4.5 min) and grooming (3.5 vs. 1.2 min, 95% CI: 1.9–5.7 vs. 0.5–2.3 min). Our study is the first to characterize stationary brush use in weaned dairy heifers. We conclude that, despite lacking previous experience, heifers use brushes for both grooming and oral manipulation.     

Effects of feeding supplemental organic iron to late gestation and early lactation dairy cows

The objectives of this experiment were to determine the Fe status of cows in late gestation and early lactation and determine whether measures of Fe status and milk production were affected by feeding supplemental organic Fe. Starting 60 d before anticipated calving, cows and heifers were fed diets with 0 or 30 mg/kg of supplemental Fe (Availa-Fe, Zinpro Corp., Eden Prairie, MN). All animals changed to prefresh diets at 14 d before anticipated calving and then to lactation diets following calving; the Fe supplementation rates (0 or 30 mg/kg) remained constant. The experiment ended at 63 d in milk. Hematocrit, hemoglobin, serum Fe, unsaturated Fe binding capacity, and percentage Fe binding saturation were measured at the start of the experiment, 7 d before calving, 7 d after calving, and at 60 d in milk. Treatment did not affect any measure of Fe status and values did not change greatly over time. Milk production (averaged 41 kg/d), milk composition, and dry matter intake during early lactation (averaged 20.4 kg/d) were not affected by treatment. The somatic cell count of milk was reduced when cows were fed supplemental Fe (114,000 vs. 94,000 cells/mL). The limited response to supplemental Fe may have been because basal diets were adequate in Fe (ranged from 282 to 336 mg of Fe/kg of DM) even though most of the basal dietary Fe was provided by forages, which are generally considered poor sources of available Fe.     

Histopathology of staphylococcal mastitis in unbred dairy heifers

Histologic observations of mammary tissue samples from unbred heifers revealed that secretory parenchyma from uninfected quarters was undeveloped, exhibiting small alveoli with a limited luminal area and a large interalveolar stromal area. Tissues from quarters infected with Staphylococcus aureus were less developed, exhibiting less alveolar epithelial and luminal areas and more interalveolar stroma compared with tissues from uninfected quarters. Such quarters also demonstrated minimal secretory activity. Macroscopic and microscopic abscesses were observed in one quarter with S. aureus intramammary infection. Staphylococcus aureus-infected quarters showed greater leukocyte infiltration into mammary parenchymal components and cistern lining compared with uninfected quarters. Quarters infected with non-aureus staphylococci also exhibited greater leukocyte infiltration and greater percentages of interalveolar stroma compared with uninfected controls. Results demonstrated that presence of infection increased leukocytosis into the mammary gland and reduced secretory activity in heifers, suggesting a deleterious effect on future milk production.     

Growth and feed efficiency of pureline and crossline dairy heifers

Data on 3957 heifers from the Holstein H line, Ayrshire-based A line, and C line (crossbreds between H and A lines) were used. Growth, feed consumption, and feed efficiency from 26 to 34 wk were examined. The full model included the fixed effects of herd, year of birth, season of birth, and additive, maternal, and heterotic genetic effects with 26-wk weight as a covariate. Heterotic and maternal effects were not significant. Adjusted for the 26-wk weight covariate, H line heifers gained 3 kg more than A line heifers with C line heifers intermediate. Adjusted for 26 and 34-wk weight covariates, H line heifers ate 2 kg less TDN than A line heifers and, hence, were more efficient. Correlations among traits were estimated using the residual variance-covariance matrix from the full model. Body weight at 34 wk was correlated with 26-wk weight (r = .88) but essentially independent of rate of gain (r = .02). It was correlated with feed consumed (r = .51) and negatively associated with gain/feed consumed (r = -.25). Gain was correlated (r = .84) with gain/feed consumed but mildly so (r = .28) with feed consumed. Feed consumption was negatively correlated (r = -.25) with gain/feed consumed when the 26-wk weight covariate was included but became much larger (r = -.95) when both 26 and 34 wk weight covariates were included. Although genetic differences in feed consumption and feed efficiency of growing heifers exist, these are small and closely associated with weights and weight gains.     

Feeding and management of dairy heifers for optimal lifetime productivity

A total of 433 Holstein heifer calves were fed two different energy amounts from 6 wk of age to breeding weight to determine the effect of early nutrition and age at first calving on lifetime performance. A control group of 182 heifers was fed according to the Beltsville growth standard. A second group of 251 heifers was accelerated in growth by providing more energy during early development. Both groups of heifers were bred at a minimum weight of 340 kg. Average ages at first calving for control and accelerated heifers were 24.6 mo and 22.2 mo with corresponding 305-d first lactation unadjusted milk production values of 6985 and 6729 kg and unadjusted milk fat yields of 222 and 216 kg. Average 305-d milk production values through subsequent lactations for control and accelerated animals, were lactation 2, 7790, 7842 kg; lactation 3, 8200, 8330 kg; lactation 4, 9481, 9134 kg; lactation 5, 9865, 9588 kg; lactation 6, 9515, 10,108; lactation 7, 9661, 10,112. Average total milk yields over five lactations were 42,321 and 41,623 kg. Percentages of cows remaining in the herd after five lactations were 19 and 18 for control and accelerated animals. Reproductive problems, mastitis, and deaths accounted for 70% of cows leaving the herd and did not differ between treatment groups.     

Bacteria associated with clinical mastitis in dairy heifers

A 1-yr field investigation of clinical mastitis in heifers was carried out in 24 veterinary districts in Norway. Quarter lacteal secretions from cases that occurred prepartum or within 14 d postpartum were examined bacteriologically. The study included 1040 heifers with clinical mastitis, and the total number of quarters that were clinically affected was 1361. The organisms that were most frequently isolated from samples from these quarters were Staphylococcus aureus (44.3%), Streptococcus dysgalactiae (18.2%), Staph. aureus together with Strep. dysgalactiae (1.2%), coagulase-negative staphylococci (12.8%), Arcanobacterium pyogenes (3.5%), A. pyogenes together with Strep. dysgalactiae (0.5%) or Staph. aureus (0.4%), and Escherichia coli (6.4%). Of the coagulase-negative staphylococci, Staphylococcus simulans (53.7%), Staphylococcus hyicus (14.8%), and Staphylococcus chromogenes (14.8%) were the most prevalent species. Except for a higher relative percentage of A. pyogenes in cases that occurred before parturition (8.2%) than in cases that occurred after parturition (2.7%), no significant differences were observed in the distribution of the various organisms among prepartum and postpartum cases. Regional variations were observed in the distribution of organisms. The proportions of Staph. aureus and A. pyogenes were highest, and the proportion of coagulase-negative staphylococci was lowest, in late autumn and early winter. The proportion of E. coli was highest in summer. In heifers in which mastitis was associated with increased rectal temperature or other systemic signs, the proportion of clinically affected quarters that were infected with Staph. aureus was larger than that in heifers without systemic reaction.     

Feed bunk length requirements for Holstein dairy heifers

The objectives of this study were to determine the necessary feed bunk length per heifer and to assess the feeding behavior of heifers fed from bunks of varying sizes. Heifers in three age categories were used for three 16-wk experiments. In Experiment 1, feed bunk lengths per heifer were 15 or 31 cm, and, in Experiments 2 and 3, the lengths were 15, 31, or 47 cm per heifer. Heifers were fed a total mixed ration at restricted intakes. Within-group growth analyses showed uniform growth rates for all heifers at all feed bunk lengths. Individual heifer growth within each group did not vary significantly for either length used in Experiment 1. In Experiment 2, heifers fed from a 15-cm bunk had more variation in live weight gain than did heifers fed from 31- or 47-cm bunks. Live weight gains of heifers fed from a 31-cm bunk varied more than those of heifers fed from 15- and 47-cm bunks in Experiment 3. The mean number of eating bouts and meals and the mean meal duration showed differences between the 15-cm feed bunk length and the 31- and 47-cm feed bunk lengths in Experiments 1 and 2. In Experiment 3, this behavior was different across all lengths. Based on growth responses and feeding behavior, heifers that grow rapidly and that are fed a high quality total mixed diet in a free stall or a bedded pack group housing system require 15-, 31-, and 47-cm feed bunk lengths at 4 to 8, 11.5 to 15.5, and 17 to 21 mo of age, respectively.     

Nitrogen and phosphorus retention and excretion in late-gestation dairy heifers

The objectives of this study were to evaluate the effects of limit feeding diets containing concentrates or by-products in place of forages on manure and nutrient excretion in growing, gravid heifers. Eighteen Holstein heifers confirmed pregnant were grouped by due date and fed 1 of 3 diets (n = 6 per treatment) for the last 14 wk of pregnancy. Diets were high forage, fed ad libitum (HF); by-product based (BP), fed at the same rate as HF-fed heifers; or low forage (LF), fed at 86% of the HF diet. Diets were designed to supply equal quantities of P, N, and metabolizable energy. Total collection of feces and urine was conducted in wk 14, 10, 6, and 2 prepartum. The HF ration was 90.7% forage, 13.7% crude protein (CP), and contained orchardgrass hay, corn silage, corn grain, soybean meal 44%, and a vitamin-mineral premix. The BP diet was 46.2% forage and 14.0% CP, with 70% of the grain mix space replaced with soybean hulls and cottonseed hulls in a 1:1 ratio, with intake limited to 93% of the dry matter intake (DMI) of HF. The LF ration was 45.3% forage and 17.8% CP, with intake limited to 86% of the DMI of HF. The effect of diet was analyzed with repeated measures, using preplanned contrasts to compare HF with BP and LF with HF and BP. As designed, heifers fed HF and BP had greater DMI than the heifers limit-fed LF, and there was no effect of diet on average daily gain or BW. Intake and digestibility of N were lower, and fecal N excretion was higher, in heifers fed HF and BP than heifers fed LF. Mean feces excretion on both a wet and dry basis was greater for HF heifers compared with BP heifers and less for LF heifers than for HF and BP heifers. Despite differences in urinary output, diet had no effect on urea N excretion, but there was a trend for heifers fed HF and BP rations to excrete less urinary N compared with those fed LF. Compared with HF and BP heifers, LF heifers tended to have lower fecal P excretion and had higher urinary P excretion. Measured manure and urine excretion from heifers fed LF was greater than current American Society of Agricultural and Biological Engineers values, whereas heifers fed HF excreted less manure and urine than predicted. Heifers achieving similar rates of gain from diets differing in forage, grain, and by-product content excreted widely varying quantities of manure.     

Growth and nutrient digestion by dairy heifers fed semipurified diets

Holstein heifers, which weighed an average of 154 kg, were randomly assigned to three dietary treatments in a split plot in time design. Differences in diets were fiber source: solka floc, corn cobs, and corn silage. The major source of added protein was corn gluten meal. Total collection metabolism periods were the final 7 d of each of two 30-d periods. Several heifers had simple digestive disturbances, which appeared to be related to low ruminal pH, while consuming the solka floc diet. Average daily gains were .78, .83, and 1.02 kg/d for treatments solka floc, corn cobs, and corn silage, respectively. Gains were within the range of acceptable growth standards and were higher than reports in the literature for semipurified and purified diets. Protein in corn gluten meal appeared to be utilized efficiently by the heifers for growth. The solka floc and corn cob diets are acceptable for growing dairy heifers where a low mineral content is desired but normal growth rates need to be maintained. The solka floc diet might be improved by including a buffer to help stabilize rumen pH.