Increased milk production versus reproductive and energy status of high producing dairy cows

Two groups of 10 Holstein cows were chosen by pairs from a 20-yr genetic selection project that used either breed average or breed high sires chosen only for Predicted Differences in milk production. Milk production (305-d mature equivalent) was 10,814 kg and 6912 kg for the high and average groups of cows. Days to first visual estrus and number of ovulations before first visual estrus were greater for the high versus the average group (66 vs. 43 d and 1.6 vs. .7 ovulations). No differences were significant between groups for the interval from parturition to uterine involution or for days to first ovulation. Energy balance was less for the high group during wk 1, 2, 10, and 11. Plasma glucose concentration was lowest during wk 2 for both groups, and nonesterified fatty acids and beta-hydroxybutyrate were greatest for both groups during wk 1 and 2. Liver glycogen content was lower at d 15 postpartum for the high group, and liver triglyceride content was greater on d 30 for the high group. The data for reproductive functions support the concept that high milk production is antagonistic to expression of estrous behavior but not to reactivation of ovarian function.     

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.     

The effect of dry period duration and dietary energy density on milk production, bioenergetic status, and postpartum ovarian function in Holstein-Friesian dairy cows

Following parturition, it is typical for dairy cows to enter a period of negative energy balance and body condition loss to support mammary milk synthesis; this is associated with compromised reproductive performance. Alternative management strategies during the prepartum (dry) and early postpartum periods may ameliorate this loss. Forty mature Holstein-Friesian cows were assigned to 1 of 2 dry period treatments [standard 8-wk dry period (SDP) or no planned dry period (NDP)] and 1 of 2 dietary energy density treatments [standard TMR (STMR) or high-quality TMR (HTMR)]. Milk yield during wk 1 to 12 postpartum was reduced in cows assigned to the NDP treatment. Energy balance and body condition score (BCS) during wk 1 to 4 postpartum were increased in cows assigned to the NDP treatment compared with the cows assigned to the SDP treatment, and BCS increased from wk 5 to 12 postpartum in the NDP cows compared with the SDP cows. During the first 12 wk postpartum, cows assigned to the HTMR diet had greater milk yield and reduced milk fat concentration compared with the cows assigned the STMR diet. The BCS was greater from wk 5 to 12 postpartum in HTMR cows compared with STMR cows. During the period from wk −3 to +3 relative to parturition, circulating concentrations of insulin, glucose, and IGF-I were greater in cows in the NDP treatment compared with cows in the SDP treatment. Cows assigned to the HTMR diet had greater circulating insulin and glucose concentrations compared with the STMR cows from wk −3 to +3 relative to parturition. The first postpartum ovulation occurred earlier for cows in the NDP treatment compared with cows in the SDP treatment (16.9 vs. 24.8 d postpartum. Cows assigned to the STMR diet tended to have a higher conception rate to first service compared with cows assigned to the HTMR diet. Energy balance and metabolic status can be improved by either eliminating the dry period or by feeding a higher energy diet, but effects on the reproductive axis appear to be different.     

Chickpeas as a protein and energy supplement for high producing dairy cows

Thirty lactating Holstein cows were randomly assigned to one of three diets to evaluate chickpeas as dietary supplement from wk 4 to 16 postpartum. Diets contained chickpeas at 0, 50, and 100% of the concentrate DM in place of corn and soybean meal. Total mixed diets, fed individually, contained concentrate, corn silage, and alfalfa hay at 52, 32, and 16% of DM. Milk yield (34.5, 35.1, 35.7 kg/d) was higher for cows fed 100% chickpeas than 0% chickpeas. Milk medium-chain (C12 to C16) fatty acids (53.8, 48.6, 45.5 g/100 g fat), milk long-chain (C18) fatty acids (29.4, 35.0, 38.8 g/100 g fat), and milk protein (3.20, 3.09, 2.96%) differed for all three diets. Ruminal acetate: propionate (2.0, 2.0, 2.4) was highest for cows fed 100% chickpeas. Total essential amino acid concentration in blood serum (105.3, 95.9, 89.4 mumol/dl) was higher for cows fed 0% chickpeas than 100% chickpeas. Lactational responses are discussed with respect to increased intake of fat, increased degradability of dietary protein, and decreased plasma essential amino acids.     

The relationships between early lactation energy status indicators and endocrine fertility traits in dairy cows

The relationships between dairy cow milk-based energy status (ES) indicators and fertility traits were studied during periods 8 to 21, 22 to 35, 36 to 49, and 50 to 63 d in milk. Commencement of luteal activity (C-LA) and interval from calving to the first heat (CFH), based on frequent measurements of progesterone by the management tool Herd Navigator (DeLaval), were used as fertility traits. Energy status indicator traits were milk β-hydroxybutyrate (BHB) concentration provided by Herd Navigator and milk fat:protein ratio, concentration of C18:1 cis-9, the ratio of fatty acids (FA) C18:1 cis-9 and C10:0 in test-day milk samples, and predicted plasma concentration of nonesterified fatty acids (NEFA) on test days. Plasma NEFA predictions were based either directly on milk mid-infrared spectra (MIR) or on milk fatty acids based on MIR spectra (NEFA_mir and NEFA_fa, respectively). The average (standard deviation) C-LA was 39.3 (±16.6) days, and the average CFH was 50.7 (±17.2) days. The correlations between fertility traits and ES indicators tended to be higher for multiparous (r < 0.28) than for primiparous (r < 0.16) cows. All correlations were lower in the last period than in the other periods. In period 1, correlations of C-LA with NEFA_fa and BHB, respectively, were 0.15 and 0.14 for primiparous and 0.26 and 0.22 for multiparous cows. The associations between fertility traits and ES indicators indicated that negative ES during the first weeks postpartum may delay the onset of luteal activity. Milk FPR was not as good an indicator for cow ES as other indicators. According to these findings, predictions of plasma NEFA and milk FA based on milk MIR spectra of routine test-day samples and the frequent measurement of milk BHB by Herd Navigator gave equally good predictions of cow ES during the first weeks of lactation. Our results indicate that routinely measured milk traits can be used for ES evaluation in early lactation.     

Effect of dietary-induced increases in circulating insulin concentrations during the early postpartum period on reproductive function in dairy cows

Although it has become increasingly clear that fertility in modern dairy cattle is declining in association with increased milk yields, the underlying mechanism is poorly understood. The first ovulation post partum is delayed in dairy cows undergoing selection for genetic merit for milk yield in association with lower circulating insulin concentrations. The aim of this study was to investigate whether feeding a diet to increase circulating insulin concentrations can overcome this delay in the first ovulation post partum. The experiment was a 2 x 2 factorial design (n = 10 per group) involving diet and genetic merit for milk yield. The dietary treatment started on the day of calving and lasted for 50 days. Plasma samples were collected each day and ovarian ultra-sonography was performed three times a week during the experimental feeding period. Milk yield was recorded each day, and body weight and body condition score were determined each week. Milk samples were collected three times a week from day 50 to day 105 post partum, and reproductive performance data were recorded for all the cows as part of the routine farm practice. The dietary treatment induced significant differences in plasma insulin concentrations in both high and low genetic merit cows. Although high genetic merit cows produced more milk, lost more body weight and had lower body condition scores during the experiment, no significant effect of diet was observed on these measurements. The high insulin inducing diet increased the proportion of cows ovulating within 50 days of calving and reduced the intervals from calving to first ovulation, and tended to reduce the intervals from calving to first service and to conception. These fertility parameters were also more favourable in low than in high genetic merit cows, but no interaction between diet and genetic merit was observed for any of these parameters. Genetic merit, but not diet, also affected the number of services required per conception and the conception rate. In conclusion, these results have confirmed that genetic selection for high milk yield is associated with a decrease in reproductive performance in dairy cows. More importantly, this study has demonstrated that it is possible to alleviate this problem by nutritional manipulation.     

Relationship of plasma nonesterified fatty acids and walking activity in postpartum dairy cows

To survive and produce milk, postpartum dairy cows use their reserves through lipolysis. If the negative energy balance is severe, nonesterified fatty acids (NEFA) are formed that can impair several physiological processes. A pilot study suggested that increased walking activity after calving may be related to a reduced serum concentration of NEFA. The objective of this study was to determine the relationship between plasma concentrations of NEFA and walking activity in dairy cattle during the postpartum period. Data were collected from 33 multiparous Holstein-Friesian dairy cows. Walking activities were quantified using pedometry, and blood samples were collected for determination of NEFA. Results of this study indicated that a negative relationship existed between walking activity and plasma NEFA concentrations in postpartum dairy cows.     

Short communication: Relationship between metabolic status and the milk concentrations of haptoglobin and lactoferrin in dairy cows during early lactation

To investigate the relationship between metabolic status and the acute phase proteins haptoglobin (Hp) and lactoferrin (Lf) in milk, the concentrations of β-hydroxybutyrate (BHBA), nonesterified fatty acids (NEFA) and Hp were determined in blood samples collected weekly from 4 wk prepartum until 12 wk postpartum. Haptoglobin and Lf were determined in weekly milk samples. The cows (n = 49) were retrospectively classified according to NEFA and BHBA concentrations using different time intervals and threshold values for NEFA and BHBA, respectively. For BHBA, 4 threshold concentrations, (0.8, 1.0, 1.2, and 1.6 mM) were evaluated either at the first week before calving, at wk 1 or 2 postpartum, or when considering the means of wk 2 and 3 postpartum. For NEFA, the tested thresholds were 0.5 and 0.6 mM at wk 1 prepartum, wk 1 or 2 postpartum, or the means of wk 1 and 2 postpartum. All variables showed changes during the interval of observation. Comparing the time course of the acute phase proteins in the subgroups classified according to BHBA or NEFA, consistently greater concentrations of Hp in serum and milk and of Lf in milk were observed in those animals with BHBA concentrations above 1.6 mM during the last week before calving (n = 3/47) than in those with BHBA concentrations below this threshold. For NEFA, analogous differences for Hp in both serum and milk (0.52 ± 0.07 and 18.1 ± 4.6 for NEFA >0.6 mM vs. 0.36 ± 0.04 mg/mL and 8.46 ± 1.63 &micro;g/mL for NEFA <0.6 mM, respectively) and for Lf in milk (130 ± 8.5 vs. 89.2 ± 7.1 &micro;g/mL, respectively) were detected when a threshold of 0.6 mM at wk 2 postpartum was used. Our results indicated that cows having BHBA and NEFA serum concentrations above these thresholds at defined times could be identified.     

Association between early postpartum rumination time and peak milk yield in dairy cows

Limited information is available on the relationship between rumination time (RT) in the early postpartum period and milk production later in lactation. Therefore, the objectives of this study were to (1) investigate the association of change in RT and average RT during the immediate postpartum period with peak milk yield (PMY) in dairy cows, and (2) determine the best model based on days in milk (DIM) to evaluate this association. Cows from 33 free-flow automatic milking system farms were included in this study, where retrospective milk production and RT data were collected for 12 mo. Cows were categorized by parity number into parity 1 (P1, n = 1,538), parity 2 (P2, n = 1,354), or parity ≥3 (P3+, n = 1,770). For each cow, PMY was identified as the highest daily milk yield up to 180 DIM for P1 and 120 DIM for P2 and P3+ cows. Five change in RT variables and 5 average RT variables were created corresponding to the first 2 to 6 DIM. Change in RT variables were the slope coefficients for change in RT/d related to DIM = 1 extracted from simple linear regressions, and average RT variables were the arithmetic mean RT. Five models analyzing PMY and corresponding variables calculated over the first 2 to 6 DIM had fixed effects of average RT, change in RT, parity, average RT × parity interaction, change in RT × parity interaction, and a random intercept for farm. Peak milk yield occurred at (median) 75, 44, and 46 DIM for P1, P2, and P3+, respectively. Overall PMY was (mean ± standard deviation) 54 ± 11 kg and it increased as parity increased. A positive association was found between change in RT and PMY, and average RT and PMY for P2 and P3+ cows in all 5 models corresponding to the first 2 to 6 DIM, indicating that greater average RT and quicker increase in RT after calving are associated with greater PMY for multiparous cows. Although the model including all 6 DIM had the greatest accuracy, results indicated that rumination data collected over the first 2 DIM may also provide adequate information for the association of average RT and change in RT with PMY in P2 and P3+ cows. For each 100 min/d increase in change in RT over the first 6 DIM, PMY increased by 4.3 (95% confidence interval: 2.2–6.3) and 4.8 (95% confidence interval: 3.2–6.5) kg for P2 and P3+ cows, respectively. Peak milk yield increased by 2.3 (95% CI: 1.7–2.8) and 2.2 (95% confidence interval: 1.7–2.6) kg for each 100 min increase in average RT over the first 6 DIM for P2 and P3+ cows, respectively. No association was observed between rumination behaviors and PMY for P1 cows. Results from this study indicate that the length of time for multiparous cows to achieve a stable RT in the early postpartum period combined with average RT during the same period may be useful in predicting their overall lactation milk production.     

Associations of cytological endometritis with energy metabolism and inflammation during the periparturient period and early lactation in dairy cows

Multiparous Holstein cows (n = 108) were used to determine the associations of cytological endometritis (CE) with plasma nonesterified fatty acids (NEFA) and β-hydroxybutyrate (BHBA) as markers of energy metabolism, calculated energy balance (EB), and plasma haptoglobin (Hp) as a marker of inflammation during the periparturient period and early lactation. Evaluation of endometrial cytology by low-volume uterine lavage was conducted on 1 d between 40 and 60 d postcalving. The incidence of CE among cows sampled was 40%. The area under the curve (AUC) was calculated for both NEFA and BHBA using data collected from 3 wk before to 3 wk after parturition. Data for NEFA and BHBA AUC were stratified into prepartum (wk −3 to parturition) and postpartum (parturition to wk +3) for statistical analysis. Prepartum AUC for neither NEFA nor BHBA was associated with subsequent CE; however, cows that subsequently developed CE tended to have higher postpartum AUC for NEFA and had higher postpartum AUC for BHBA. Consistent with the results for plasma NEFA and BHBA, calculated EB during the prepartum period was not different in cows that did or did not develop CE; however, cows with CE had lower EB during the 6-wk postpartum period compared with cows without CE. Analysis of EB by week (wk −3 to −1 before calving and wk +1 to +6 postcalving) indicated that EB in cows with CE was lower at wk +1, +2, and +3 and tended to be lower at wk +6 than cows without CE. Plasma Hp concentrations were analyzed from wk +1 to +8 of lactation; concentrations of Hp were not different during either wk +1 or the entire postpartum period between cows that did or did not develop CE. These results suggest that lower energy status during the first 3 wk postpartum, but not necessarily systemic inflammation, is associated with subsequent development of CE.     

Effects of pasture feeding during the periparturient period on postpartum anovulation in grazed dairy cows

Extended postpartum anovulatory intervals (PPAI) are a major contributor to infertility in seasonal dairy systems constrained to 365-d calving intervals. This study was conducted to evaluate the effects of pasture-based dietary energy intakes during the transitional calving period on PPAI. Sixty-eight multiparous Holstein-Friesian cows were assigned to high [11.9 kg of dry matter (DM)/d] or low (4.8 kg of DM/d) pasture intakes for 29 ± 7.7 d prepartum. After calving, cows within each prepartum diet were assigned to either a high (13.5 kg of DM/d) or low (8.6 kg of DM/d) pasture intake for 35 d in a 2 × 2 factorial arrangement. Progesterone concentrations were measured in milk samples collected twice weekly to determine PPAI, which was defined as the day on which progesterone level was elevated to ≥3 ng/mL with subsequent concentrations being consistent with an ovulatory cycle. Blood samples were collected before initiation of treatments, and at d −21, −14, −7, 0 (day of calving), 1, 2, 3, 4, 7, 14, 21, 28, and 35 in all cows. The PPAI was associated with body condition score, concentrations of plasma insulin and insulin-like growth factor-I, and growth hormone. Postpartum intake did not affect these metabolic hormones or PPAI, but yield of FCM during the first 35 d was reduced by 23% among cows on a restricted intake. No relationships were found between PPAI and milk production characteristics. These data demonstrate that when pasture is the sole dietary source during the calving transition period, PPAI may be influenced by prepartum intake levels, whereas postpartum intake influences milk yield, but not PPAI. The underlying mechanism(s) that associates the prepartum period to PPAI may involve the sensitivity of the growth hormone-insulin-like growth factor axis to dietary intake levels. Nonetheless, PPAI in grazing multiparous dairy cows appears largely unresponsive to intake levels during the calving transition period.     

Lying behavior and postpartum health status in grazing dairy cows

Many cows have difficulty making the transition from pregnancy to lactation, as evidenced by the high incidence of disease that occurs in the weeks after calving. Changes in lying behavior can be used as an indicator of illness, yet no work to date has evaluated this relationship in dairy cows on pasture. The objectives of this study were to describe the lying behavior of grazing dairy cows during the first 3 wk after calving and determine the relationships between transition diseases and lying behavior. Our convenience sample included 227 multiparous and 47 primiparous Holstein cows from 6 commercial farms. Cows were recruited as they calved during the spring calving period. Electronic data loggers (Hobo Pendant G Acceleration, Onset Computer Corp., Pocasset, MA) recorded lying behavior at 1-min intervals. Diseases were recorded up to 21 d in milk, and cows were subsequently categorized into 3 health categories: (1) healthy, not lame and had no other signs of clinical (retained placenta, milk fever, metritis, mastitis) or subclinical (ketosis, hypocalcemia) postpartum diseases; (2) lame, identified as being clinically or severely lame with no other signs of clinical or subclinical postpartum disease; and (3) sick, diagnosed as having one or more clinical postpartum diseases (with or without a subclinical disease) but not lame. This last group was further divided into 2 groups: those that were diagnosed with a single clinical health event and those diagnosed with more than one clinical event. Lying behavior differed between primiparous and multiparous cows; primiparous cows divided their lying time into more bouts than did multiparous cows (9.7 ± 0.54 vs. 8.4 ± 0.26 bouts/d) and spent less time lying down than multiparous cows (7.5 ± 0.38 h/d vs. 8.5 ± 0.19 h/d). Lying behavior was also affected by illness; primiparous cows that developed more than one clinical disease, excluding lameness, spent more time lying, and tended to have longer lying bouts in the days following calving compared with healthy cows; multiparous severely lame cows spent more time lying down (1.7 h longer per day) compared with multiparous cows that were nonlame. Clinically lame cows had fewer lying bouts per day and these bouts were of longer duration than healthy nonlame cows. In summary, changes in lying behavior after calving were associated with postpartum health status in grazing dairy cows.     

Diet starch concentration and starch fermentability affect energy intake and energy balance of cows in the early postpartum period

Our objective was to evaluate the effects of diet starch concentration and fermentability on energy intake and energy balance during the early postpartum (PP) period. Fifty-two multiparous Holstein cows were used in a randomized block design experiment with a 2 × 2 factorial arrangement of treatments. Treatment rations were formulated to 22% or 28% starch concentration (LS and HS, respectively) with dry ground corn (DGC) or high moisture corn (HMC) as the primary starch source. Rations were formulated for 22% forage neutral detergent fiber (NDF) and 17% crude protein and fed from 1 to 23 d PP. Starch concentration was adjusted by altering concentrations of corn grain and soyhulls. Dry matter intake and milk yield were measured daily, and milk components, milk composition, body condition score (BCS), body weight (BW), and back fat thickness (BFT) were measured weekly. Feeds and refusals as well as fecal samples were collected, and digestibility was determined weekly. High moisture corn (HMC) decreased dry matter and net energy (NE_L) intakes compared with DGC more when included in an HS diet (3.9 kg/d and 3.2 Mcal/d) than in an LS diet (0.9 kg/d and 0.6 Mcal/d). The HMC treatment decreased NDF digestibility 3.7 percentage units compared with DGC when included in the HS diet but had little effect when included in an LS diet. Compared with DGC, HMC increased weekly BW and BFT loss when included in an HS diet (−34.7 vs. −8.4 kg/wk and −0.12 vs. −0.10 cm/wk) and decreased weekly BW loss but increased weekly BFT loss when included in an LS diet (−18.9 vs. −21.4 kg/wk and −0.11 vs. −0.02 cm/wk). Weekly BCS loss increased for HMC compared with DGC (−0.33 vs. −0.23 unit/wk). High moisture corn also decreased milk NE_L output compared with DGC (28.2 vs. 31 Mcal/d), but had little effect on energy balance, which was improved by HS compared with LS (−14.7 vs. −16.8 Mcal/d). Over time, concentrations of milk de novo fatty acids (<16 carbons) increased and concentration of milk preformed fatty acids (>16 carbons) decreased for all treatments, but yields of both sources as well as yield of mixed fatty acids (C16:0 plus C16:1 cis-9 and iso-C16:0) decreased over time with increased SF. Feeding HMC decreased energy intake and milk energy output, but it had little effect on energy balance during the early PP period.     

Effects of grain processing and bovine somatotropin on metabolism and ovarian activity of dairy cows during early lactation

This study compared the effects of exogenous bovine somatotropin (bST) on the metabolism and ovarian activity of cows fed diets differing in ruminally degradable starch. Twenty-four multiparous and eight primiparous Holstein cows in early lactation were divided into four groups and fed diets containing 39% grain as steam-flaked sorghum or steam-rolled corn with or without bST for 90 d in a 2 x 2 factorial design. Flaked sorghum improved energy status of cows during early lactation, tending to increase plasma glucose and insulin. Administration of bST decreased plasma urea nitrogen and increased nonesterified fatty acids (NEFA). Plasma levels of beta-hydroxybutyrate (BHBA) and hepatic concentrations of triglycerides were not altered by treatments. Temporal changes in plasma glucose, urea nitrogen, NEFA, and BHBA were detected in a quadratic manner and insulin increased linearly with time, but treatments did not affect postpartum changes in these metabolites. There were greater decreases in body weight and net energy balance in cows on bST during the first 7 wk of treatment. Cows receiving bST took longer to reach the nadir of negative energy balance, and bST tended to delay the period to reach a positive energy balance. Follicular populations and incidence of cystic ovaries were not affected by treatments, but cows receiving bST had fewer double ovulations. Flaked sorghum increased plasma progesterone during the early luteal phase of the first two postpartum estrous cycles. Feeding more ruminally degradable starch improved the energy status and luteal activity of cows in early lactation.     

Energy balance and size and number of ovarian follicles detected by ultrasonography in early postpartum dairy cows

Multiparous Holstein cows (n = 52) were fed one of six diets consisting of a totally mixed ration (corn silage, corn grain, soybean meal, dried distillers grains, and whole cottonseed) plus either alfalfa hay, alfalfa cubes, or bermuda-grass hay fed chopped as a component in the mixed ration or separate as long hay. Predicted energy balance was calculated from DM intake, milk yield and composition, and BW. On d 25 postpartum, ovarian status was programmed by injecting 25 mg of prostaglandin F2 alpha and treating cows for 15 d with an intravaginal device containing 1.9 g progesterone. Before d 25, number of class 1 follicles (3 to 5 mm; detected by ultrasonography) decreased with increasing days postpartum, and number of class 3 (10 to 15 mm) and class 4 (greater than 15 mm) follicles increased. The number of class 1 and 2 follicles (6 to 9 mm) decreased with increasing energy balance, and number of class 3 follicles increased with energy balance. Before d 25, predicted energy balance explained treatment differences in the number of follicles within each size class. After d 25, energy balance did not affect the average number of follicles per cow, but diet affected the number of follicles within each class. Predicted energy balance and dietary treatments influenced number of follicles at different times after calving. These results identify the importance of diet and energy balance to follicular and ovarian function in postpartum lactating dairy cows.     

Effects of milk production capacity and metabolic status on HPA function in early postpartum dairy cows

Increasing milk yields in modern dairy cows cause concern that high yield may impair the cows' health and welfare, for example, via negative effects on metabolic status and hypothalamo-pituitary-adrenocortical (HPA) function. This study aims to investigate whether a high level of milk production, and the associated metabolic status, affects HPA function in dairy cows and changes their adaptive capacity. Additionally, it aims to establish whether possible effects of milk production level only show under challenging conditions. Holstein-Friesian cows, which produced on average 11,443 and 7727 kg of fat and protein-corrected milk (FPCM)/305 d in their previous lactation, were compared. During the dry period, the cows were fed to requirements or overfed. High milk yield and the concomitant large energy deficit were associated with 1) increased pituitary (re)activity, i.e., increased ACTH baseline concentrations and higher ACTH concentrations after corticotropin-releasing hormone (CRH) administration, and 2) decreased adrenocortical reactivity, i.e., lower cortisol responses after ACTH administration. Although significant, the effects of milk production level on HPA function were relatively small. Animals showed seemingly normal hormonal responses to CRH and ACTH administration. Also, cortisol baseline concentrations were unaffected. It seems, therefore, unlikely that the adaptive capacity of the high-producing cows was significantly impaired compared with their low-producing herdmates.     

Lying behavior and activity during the transition period of clinically healthy grazing dairy cows

Lying behavior and activity may provide useful information for the prediction of an imminent calving and the health of transition dairy cows; however, it is important first to understand what constitutes typical lying behavior and activity because this has not been defined for grazing dairy cows during the transition period. Our objective was to describe changes in lying behavior and activity in grazing dairy cows during the transition period using varying phenotypes typical of commercial dairy herds under grazing systems. Behavior data from IceTag or IceQube (IceRobotics, Edinburgh, Scotland) triaxial accelerometers were collected for 310 cow parities from multiparous, mixed-age (mean ± standard deviation; 4.5 ± 1.65 yr), and mixed-breed [Holstein-Friesian (HF), n = 216; and HF × Jersey, n = 94] grazing dairy cows from 4 parent experiments. The IceTags or IceQubes captured lying and activity data during the transition period (−21 to 34 d relative to calving) to allow the calculation of daily lying time (h/d), daily lying bouts (LB; no./d), mean LB duration (min/bout), and the number of steps taken (steps/d). Lying behavior and activity were analyzed using a repeated measures ANOVA during 3 periods: PRE (−21 to −3 d), POST (3 to 21 d), and the day of calving (d 0). Lying time was lower on d 0 (7.25 h/d) compared with PRE and POST lying times (10.3 and 8.58 h/d, respectively), with more frequent LB on d 0 (12.9 no./d) compared with the PRE and POST daily LB (8.15 vs. 7.74 no./d). Cows took more steps POST (4,424 steps/d) compared with d 0 and PRE (4,105 and 2,289 steps/d, respectively). Regression analysis determined that daily lying time decreased substantially from −3 to 0 d (slope = −1.03 ± 0.07 h/d) and from −2 and −1 d for daily LB (slope = 5.09 ± 0.54 no./d), which may be due to the calving event itself but also reflect restlessness. Daily lying time, daily LB, LB duration, and number of steps taken were substantially altered at the time of the calving event in grazing dairy cows. Cows were more active, spent less time lying, and took more steps postcalving compared with precalving, and it appears that this behavior may largely be due to activity associated with twice daily milking. Mean lying behavior and activity measures were more highly variable across individuals than across groups. Information available via activity monitors may contribute to the improvement of individual management of transition dairy cows, and this research provides a benchmark for typical changes in behavior during the transition period in grazing systems.     

Temporary alterations to postpartum milking frequency affect whole-lactation milk production and the energy status of pasture-grazed dairy cows

This study investigated the immediate and long-term effects of temporary alterations to postpartum milking frequency (MF) on milk production, body condition score (BCS), and indicators of energy status in pasture-grazed cows supplemented with concentrates. Multiparous Holstein-Friesian cows (n = 150) were randomly assigned to 1 of 5 groups at calving: milked twice daily (2×) throughout lactation (control), or milked either once daily (1×) or 3 times daily (3×) for 3 or 6 wk immediately postpartum, and then 2× for the remainder of lactation. During wk 1 to 3 postpartum, cows milked 1× produced 15% less milk and 17% less energy-corrected milk (ECM) than cows milked 2×. This immediate production loss increased to 20% less milk and 22% less ECM during wk 4 to 6 postpartum for cows that remained on 1× milking; these animals also produced less than 1× cows switched to 2× milking after 3 wk. During wk 8 to 32, when all cows were milked 2×, those previously milked 1× had sustained reductions in milk (−6%) and ECM (−8%) yields, which were not affected by the duration of reduced postpartum MF. In contrast, cows milked 3× postpartum had 7% greater milk yields during wk 1 to 6 compared with 2× controls, irrespective of the duration of increased MF. Milk yields also remained numerically greater (+5%) during wk 8 to 32 in cows previously milked 3×. Nevertheless, yields of ECM were not increased by 3× milking, because of lower milk fat and protein contents that persisted for the rest of lactation. In addition, indicators of cow energy status reflected an increasing state of negative energy balance with increasing MF. Cows milked 1× postpartum had greater plasma glucose and lower plasma nonesterified fatty acid concentrations during the reduced MF, and plasma glucose remained lower for 2 wk after cows had switched to 2× milking. Moreover, BCS was improved relative to 2× controls from wk 5 to 6. In contrast, cows milked 3× had lower plasma glucose concentrations, greater plasma nonesterified fatty acid concentrations, and greater BCS loss during wk 1 to 3; however, greater body fat mobilization was not sustained, indicating that additional energy supplements may be required to achieve better milk production responses. In conclusion, temporary 1× milking had lactation-long negative effects on milk and milk component yields but improved cow energy status and BCS, whereas temporary 3× milking immediately increased milk yield but did not improve milk fat and protein yields in pasture-grazed cows.     

Short communication: Relationship between methods for measurement of serum electrolytes and the relationship between ionized and total calcium and neutrophil oxidative burst activity in early postpartum dairy cows

The objectives of this study were to (1) compare a test for serum measurement of total Ca (tCa), Mg, and P (VetTest Chemistry Analyzer, IDEXX Laboratories Inc., Westbrook, ME) to reference methods (spectrophotometric assays on a Beckman Coulter 640e automated clinical chemistry analyzer; Beckman Coulter, Brea, CA), (2) determine the relationship between ionized Ca (iCa) and reference method tCa in the immediate postpartum period, and (3) assess the relative value of these blood Ca indices as predictors of neutrophil oxidative burst activity. Samples were collected from multiparous Holstein cows (n = 33) over the first 5 d in milk. A total of 183 samples for objective 1 and 181 samples for objective 2 were available. Neutrophil oxidative burst activity was assessed once between 2 and 5 d in milk (n = 29). Linear regression demonstrated strong relationships between serum tCa, Mg, and P concentrations measured by the VetTest compared with the reference method. Bland Altman analysis indicated that the VetTest values were higher than the reference method by 0.22 mmol/L for tCa, 0.12 mmol/L for Mg, and 0.16 mmol/L for P. Compared with hypocalcemia categorized at ≤2.0 or ≤2.125 mmol/L with the reference method tCa, thresholds for the VetTest measured tCa of ≤2.23 mmol/L (sensitivity = 87%, specificity = 89%) or ≤2.30 mmol/L (sensitivity = 86%, specificity = 96%) could be used. The relationship between whole-blood iCa and reference method serum tCa differed by sampling time point after calving. Compared with identification of hypocalcemia with serum tCa measurements from the reference method (thresholds of ≤2.0 and 2.125 mmol/L), a whole-blood iCa threshold of ≤1.17 mmol/L resulted in the highest combined sensitivities (94 and 82%) and specificities (80 and 94%) at either threshold. Ionized Ca measurements were more consistently related to outcomes of neutrophil oxidative burst activity measured in vitro. The VetTest measurements of serum tCa reliably identified hypocalcemia when thresholds were adjusted to account for the bias of the test. The variation in the relationship between iCa and reference method tCa in the days following parturition suggest that these measures cannot be used interchangeably as indicators of Ca status. The more consistent associations between iCa and in vitro measures of neutrophil function, compared with tCa, indicated that this may be a more sensitive predictor of functional outcomes associated with postpartum Ca status.     

Relationships between endometritis and metabolic state during the transition period in pasture-grazed dairy cows

The primary objective of this study was to identify relationships between endometritis and metabolic state during the calving transition and early lactation periods. A subset of mixed age and breed dairy cows (n = 78) from a seasonal, pasture-grazed herd of 389 cows was examined. The selected cows were grouped as having endometritis at d 42 postpartum or being unaffected by endometritis. Endometritis was defined as >6% (upper quartile) of uterine nucleated cells being polymorphonuclear cells (H-PMN; n = 38); unaffected by endometritis was defined as ≤1% of nucleated cells being polymorphonuclear (L-PMN; n = 40). Milk yield was determined at each milking, and milk composition (fat and protein) was determined at 2-wk intervals. Blood samples collected on d −14, 0 (d of calving), 4, 7, 14, 28, and 42 were analyzed for indicators of energy status (nonesterified fatty acids, glucose, and urea), liver function (albumin, globulin, glutamate dehydrogenase, and aspartate aminotransferase), inflammation (haptoglobin), and mineral status (Ca and Mg). Samples collected weekly from d 21 to 63 or 70 were analyzed for progesterone content. The postpartum anovulatory interval was defined to end on the first day postpartum that plasma progesterone concentration was ≥1 ng/mL. A greater percentage of H-PMN cows failed to ovulate before d 63 or 70 (34%) compared with L-PMN cows (10%), although the proportions of cows ovulating within either polymorphonuclear group was similar through d 56 postpartum. Plasma concentrations of albumin and the albumin:globulin ratio were consistently lower in H-PMN cows. Plasma Mg was lower, whereas glutamate dehydrogenase and aspartate aminotransferase were higher, in H-PMN cows during early lactation compared with L-PMN cows. Circulating metabolites indicative of energy status (nonesterified fatty acids, glucose, and urea) were not different between polymorphonuclear groups. Among 3- to 5-yr-old cows, daily milk yield for the first 42 d after calving was lower for H-PMN cows than for L-PMN cows. Among cows >5 yr old, protein percentage was lower in H-PMN cows compared with L-PMN cows. In summary, endometritis at 42 d postpartum in the herd studied was associated with an increased likelihood of remaining anovulatory. These cows had lower albumin concentrations throughout the calving transition period, perhaps indicating impaired liver function, with lower plasma Mg and evidence of hepatocellular damage in early lactation. Similar profiles of nonesterified fatty acids and glucose indicated that energy status was not a risk factor for endometritis.