Maternal heat stress reduces body and organ growth in calves: Relationship to immune status.

Late-gestation heat stress of dairy cows reduces fetal growth and influences postnatal performance and immune status of the offspring. Our first objective was to evaluate the effect of in utero heat stress on overall fetal and organ growth, particularly organs associated with immune function. The second objective was to examine the cellular mechanism of altered passive immunity in neonatal bull calves after in utero heat stress. Specifically, we examined the rate of apoptosis of intestinal cells early in life, as it is associated with gut closure. Dams were dried off approximately 45 d before expected calving and randomly assigned to 1 of 2 treatments: heat stress (HT) or cooling (CL). During the dry period all cows were housed under shade in a freestall barn, where the pen for CL cows was equipped with active cooling, including water soakers and fans, whereas the pen for HT cows had no soakers or fans. Using rectal temperature and respiration rate as indicators, heat stress was severe. Average rectal temperature in HT cows was 39.3°C compared with 39.0°C in CL cows, and HT cows had a respiration rate of 66.7 breaths/min compared with 43.2 breaths/min for CL cows. Bull calves (n = 30) were immediately separated from their dams at birth, weighed, and then killed before colostrum feeding (n = 5/treatment; d 0) or at 1 or 2 d of age following colostrum feeding (n = 5/treatment per day). After slaughter, the small intestine was removed and weighed, and samples from the jejunum were fixed for immunohistochemistry. Birth weight of bulls from HT dams was 1.1 kg lower than that of bulls from CL dams. Thymus, spleen, and heart weights of HT bulls were lower relative to those of CL bulls, whereas liver weight of HT bulls tended to be lower relative to that of CL bulls. Jejunal cell apoptosis decreased with age in both HT and CL calves after birth, mirroring gut closure. However, in utero heat stress increased the apoptotic rate in the jejunum, particularly at birth. We conclude that the chronic exposure to heat strain of HT compared with CL dams in late gestation significantly affected fetal growth and immune tissue development, which may be associated with reduced immune function in early life. Also, late-gestation heat stress increased calves' intestinal apoptosis in the first 2 d of life, which might explain the decreased IgG uptake and limited passive immune competence observed in previous studies.

In utero exposure to heat stress during late gestation has prolonged effects on the activity patterns and growth of dairy calves.

Exposure to heat stress during late gestation exerts negative carryover effects on the postnatal performance of the calf. In this study, we evaluated the health, growth, and activity patterns of calves born to cows exposed to heat stress (HT, provided only shade, n = 31) or cooling (CL, fans, soakers, and shade, n = 29) during late gestation (∼46 d, maternal dry period). Calves' body weight, rectal temperature, suckling reflex, and movement scores were recorded at birth, and calves were fed 6.6 L of maternal colostrum in 2 meals. Blood samples were collected at birth (before feeding), 24 h after birth, and at d 10 and 28 of age. Calves were housed in individual pens, fed pasteurized milk (6 L/d), and had ad libitum access to grain and water until weaning (49 d). Activity was assessed during the first week of life (wk 1), at weaning (wk 7), and in the first week postweaning (wk 8) using electronic data loggers. Health and body weight were monitored weekly. At birth, calves born to CL cows were heavier (41.9 vs. 39.1 ± 0.8 kg), their temperature was lower (38.9 vs. 39.3 ± 0.08°C), and they were more efficient at absorbing IgG than HT calves. Suckling reflex and movement score at birth were not different between groups, but calves born to CL cows spent more time (50 min/d) standing in the first week of life as a result of longer standing bouts. In wk 7 and 8, calves born to CL cows had less frequent standing bouts than HT heifers, but CL heifers maintained greater total daily standing time (36 min/d) due to longer (7 min/bout) standing bouts. All calves were healthy, but HT heifers tended to have higher (looser) fecal scores on d 10. Heifers born from CL cows gained 0.2 kg/d more from birth to weaning, weighed 4 kg more at weaning, and had greater concentrations of IGF-1 than HT calves, particularly on d 28. In utero heat stress during late gestation had immediate and prolonged effects on passive immunity, growth, and activity patterns in dairy calves.

Short communication: Effect of maternal heat stress in late gestation on blood hormones and metabolites of newborn calves.

Maternal heat stress alters immune function of the offspring, as well as metabolism and future lactational performance, but its effect on the hormonal and metabolic responses of the neonate immediately after birth is still not clear. The objective of this study was to investigate the blood profiles of hormones and metabolites of calves born to cows that were cooled (CL) or heat-stressed (HS) during the dry period. Within 2 h after birth, but before colostrum feeding, blood samples were collected from calves [18 bulls (HS: n=10; CL: n=8) and 20 heifers (HS: n=10; CL: n=10)] born to CL or HS dry cows, and hematocrit and plasma concentrations of total protein, prolactin, insulin-like growth factor-I, insulin, glucose, nonesterified fatty acid, and ß-hydroxybutyrate were measured. Compared with CL, HS calves had lower hematocrit and tended to have lower plasma concentrations of insulin, prolactin, and insulin-like growth factor-I. However, maternal heat stress had no effect on plasma levels of total protein, glucose, fatty acid, and ß-hydroxybutyrate immediately after birth. These results suggest that maternal heat stress desensitizes a calf's stress response and alters the fetal development by reducing the secretion of insulin-like growth factor-I, prolactin, and insulin.

Effect of maternal heat stress during the dry period on growth and metabolism of calves.

Preliminary studies suggest that maternal heat stress (HS) during late gestation exerts carryover effects on a calf's insulin response after weaning, but a comprehensive evaluation of how maternal HS affects calf intake, growth, and metabolic response from birth to weaning is lacking. Our objective was to evaluate the effects of maternal HS during the dry period on dry matter intake, growth, and metabolism from birth to weaning. After birth, 20 heifers born to either HS (n=10) or cooled (CL, n=10) dry cows were immediately separated from their dams and fed 3.8 L of colostrum from a common pool within 4h of birth. All heifers were managed identically and weaned at 49 d of age (DOA). Calf starter intake was recorded daily, and body weight was assessed at birth and every 2 wk from birth to 56 DOA. Blood samples were collected twice a week until 56 DOA to assess hematocrit and concentrations of insulin and metabolites. To evaluate metabolic responses to maternal HS, a glucose tolerance test, insulin, and epinephrine challenge were performed on 3 consecutive days for all heifers at 8, 29, and 57 DOA. Maternal HS during the dry period did not affect heifer birth weight. Compared with HS, CL calves consumed more starter (0.53 vs. 0.34kg/d) from birth to 56 DOA and were heavier (71.7 vs. 61.4kg) at 56 DOA. Relative to HS calves, CL calves tended to have higher hematocrit (27.4 vs. 24.7%). No differences were found between treatments in plasma concentrations of insulin and glucose, but HS calves had higher nonesterified fatty acids and ß-hydroxybutyrate concentrations after 32 DOA. Compared with CL, HS calves had a faster glucose clearance after a glucose tolerance test and a slower insulin clearance after an insulin challenge. In conclusion, maternal HS during late gestation reduces calf starter intake and growth, alters blood metabolite profile, and increases noninsulin-dependent glucose uptake.

Short communication: Maternal heat stress during the dry period alters postnatal whole-body insulin response of calves.

Heat stress during the dry period not only negatively affects a cow's performance but also affects her offspring. Previous studies indicate that calves born to cows heat-stressed during late gestation have lower birth weight but similar overall weight gain during the prepubertal period compared with those cooled in utero. However, it is unclear if whole-body insulin response, and thus metabolism, of calves is altered in their postnatal life after in utero heat stress. The aim of the present study was to examine the effects of maternal heat stress during the dry period on whole-body insulin response of calves after weaning. Calves (10/treatment) were born to cows exposed to heat stress (HT) or cooling (CL) when dry. Calves were immediately separated from their dams and fed 3.8L of high-quality colostrum within 1h after birth and then 1.9L 12h later. All calves were fed 1.9 to 3.8L of pasteurized milk in the morning and afternoon from 2 to 42 d of age and then only in the morning until weaning at 49 d. Calf starter and water were offered ad libitum starting at 2 d of age. All calves were managed in the same manner throughout the study. All calves were subjected to a glucose tolerance test (GTT) and an insulin challenge (IC) at 55 d of age. Calves heat-stressed in utero were born lighter (40 ± 1.4 vs. 45 ± 1.4 kg) compared with CL calves. Both groups of calves had similar weaning weights (HT: 68 ± 3.2 kg; CL: 71 ± 3.3 kg) and body weight gain from birth to weaning (HT: 28 ± 2.2 kg; CL: 26 ± 2.3 kg). Compared with those cooled in utero, HT calves had a similar insulin response to GTT and insulin clearance during IC but faster glucose clearance during GTT and IC. In conclusion, in addition to impaired fetal growth, maternal heat stress during the dry period enhances the whole-body insulin response of calves after weaning, which suggests the possibility of accelerated lipogenesis and fat deposition in early life.

Short communication: Effect of heat stress during the dry period on gene expression in mammary tissue and peripheral blood mononuclear cells.

Heat stress (HT) during the dry period compromises mammary gland development, decreases future milk production, and impairs the immune status of dairy cows. Our objective was to evaluate the effect of cooling HT cows during the dry period on gene expression of the mammary gland and peripheral blood mononuclear cells (PBMC). Cows were dried off 46 d before their expected calving and assigned to 2 treatments, HT or cooling (CL). Cows in the CL group were cooled with sprinklers and fans whereas HT cows were not. After parturition, all cows were housed in a freestall barn with cooling. The PBMC were isolated at dry-off and at -20, 2, and 20 d relative to calving from a subset of cows (HT, n=9; CL, n=10), and mammary biopsies were taken at the same intervals (HT, n=7; CL, n=6) for RNA extraction. Gene expression was assessed using a custom multiplex gene expression assay based on traditional reverse transcription-PCR. Genes involved in prolactin (PRL) signaling [PRL receptor long form, PRL receptor short form, suppressor of cytokine signaling (SOCS)2, SOCS3, IGF2, IGF binding protein 5, and cyclin D1], fatty acid metabolism (acetyl-CoA carboxylase α (ACACA) and lipoprotein lipase (LPL)], and IGF1 were evaluated in mammary tissue, and genes related to fatty acid metabolism [ACACA, fatty acid synthase (FASN), and LPL], cytokine production [IL6, IL8, and tumor necrosis factor (TNF)], and IGF1 were evaluated in PBMC. No differences were observed in PRL signaling or fatty acid metabolism gene expression in the mammary gland. In PBMC, HT cows had greater mRNA expression of IGF1 and TNF during the transition period relative to CL and upregulated IL8 and downregulated FASN mRNA expression at 2 d relative to calving. We conclude that cooling HT cows during the dry period alters expression of genes involved in cytokine production and lipid metabolism in PBMC.

Effect of late-gestation maternal heat stress on growth and immune function of dairy calves.

Heat stress during the dry period affects the cow's mammary gland development, metabolism, and immunity during the transition period. However, the effect of late-gestation heat stress on calf performance and immune status is unknown. Our objective was to evaluate the effect of heat stress during the final ~45 d of gestation on growth and immune function of calves. Calves (17/treatment) were born to cows that were exposed to cooling (CL) or heat stress (HT) during the dry period. Only heifer calves (CL, n=12; HT, n=9) were used in measurements of growth and immune status after birth. Heifer calves were managed under identical conditions. All were fed 3.78 L of colostrum from their respective dams within 4 h of birth and were weaned at 2 mo of age (MOA). Body weight (BW) was obtained at weaning and then monthly until 7 MOA. Withers height (WH) was measured monthly from 3 to 7 MOA. Hematocrit and plasma total protein were assessed at birth, 1, 4, 7, 11, 14, 18, 21, 25, and 28 d of age. Total serum IgG was evaluated at 1, 4, 7, 11, 14, 18, 21, 25, and 28 d of age, and apparent efficiency of absorption was calculated. Peripheral blood mononuclear cells were isolated at 7, 28, 42, and 56 d of age, and proliferation rate was measured by (3)H-thymidine incorporation in vitro. Blood cortisol concentration was measured in the dams during the dry period and in calves in the preweaning period. Gestation length was 4d shorter for HT cows compared with CL cows. Calves from CL cows had greater BW than calves from HT cows at birth (42.5 vs. 36.5 kg). Compared with CL heifers, HT heifers had decreased weaning BW (78.5 vs. 65.9 kg) but similar BW (154.6 vs. 146.4 kg) and WH (104.8 vs. 103.4 cm) from 3 to 7 MOA. Compared with CL, heifers from HT cows had less total plasma protein (6.3 vs. 5.9 g/dL), total serum IgG (1,577.3 vs. 1,057.8 mg/dL), and apparent efficiency of absorption (33.6 vs. 19.2%), and tended to have decreased hematocrit (33 vs. 30%). Additionally, CL heifers had greater peripheral blood mononuclear cell proliferation relative to HT heifers (23.8 vs. 14.1 fold). Compared with CL, late-gestation HT did not affect the blood cortisol concentration of dams during the dry period or that of the calves in the preweaning period, but CL calves tended to have increased circulating cortisol at birth (7.6 vs. 5.7 µg/dL). We conclude that heat stress of the dam during the dry period compromises the fetal growth and immune function of offspring from birth through weaning.

Effect of cooling heat-stressed dairy cows during the dry period on insulin response.

Heat stress (HT) during the dry period affects hepatic gene expression and adipose tissue mobilization during the transition period. In addition, it is postulated that HT may alter insulin action on peripheral tissues. Our objective was to evaluate the effect of cooling heat-stressed cows during the dry period on insulin effects on peripheral tissues during the transition period. Cows were dried off 46 d before expected calving and assigned to 1 of 2 treatments: HT (n = 16) or cooling (CL, n = 16). During the dry period, the average temperature-humidity index was 78, but CL cows were cooled with sprinklers and fans, whereas HT cows were not. After calving, all cows were housed and managed under the same conditions. Rectal temperatures were measured twice daily (0730 and 1430 h) and respiration rate recorded 3 times weekly during the dry period. Dry matter intake was recorded daily from dry-off to 42 d relative to calving (DRC). Body weight and body condition score were measured weekly from dry-off to 42 DRC. Milk yield and composition were recorded daily to 42 wk postpartum. Glucose tolerance tests (GTT) and insulin challenges (IC) were performed at dry-off, -14, 7, and 28 DRC in a subset of cows (HT, n = 8; CL, n = 8). Relative to HT, CL cows had lower rectal temperatures (39.3 vs. 39.0°C) in the afternoon and respiration rate (69 vs. 48 breath/min). Cows from the cooling treatment tended to consume more feed than HT cows prepartum and postpartum. Compared with HT, CL cows gained more weight before calving but lost more weight and body condition in early lactation. Cows from the cooling treatment produced more milk than HT cows (34.0 vs. 27.7 kg/d), but treatments did not affect milk composition. Treatments did not affect circulating insulin and metabolites prepartum, but CL cows had decreased glucose, increased nonesterified fatty acid, and tended to have lower insulin concentrations in plasma postpartum compared with HT cows. Cooling prepartum HT cows did not affect the insulin responses to GTT and IC during the transition period and glucose responses to GTT and IC at -14 and 28 DRC were not affected by treatments. At 7 DRC, CL cows tended to have slower glucose clearance to GTT and weaker glucose response to IC relative to HT cows. Cows from the cooling treatment had stronger nonesterified fatty acid responses to IC postpartum but not prepartum compared with HT. In conclusion, cooling heat-stressed dairy cows in the dry period reduced insulin effects on peripheral tissues in early lactation but not in the dry period.

Effect of heat stress during the dry period on mammary gland development.

Heat stress during the dry period negatively affects hepatic metabolism and cellular immune function during the transition period, and milk production in the subsequent lactation. However, the cellular mechanisms involved in the depressed mammary gland function remain unknown. The objective of the present study was to determine the effect of heat stress during the dry period on various indices of mammary gland development of multiparous cows. Cows were dried off approximately 46 d before expected calving and randomly assigned to 2 treatments, heat stress (HT, n=15) or cooling (CL, n=14), based on mature equivalent milk production. Cows in the CL treatment were provided with sprinklers and fans that came on when ambient temperatures reached 21.1°C, whereas HT cows were housed in the same barn without fans and sprinklers. After parturition, all cows were housed in a freestall barn with cooling. Rectal temperatures were measured twice daily (0730 and 1430 h) and respiration rates recorded at 1500 h on a Monday-Wednesday-Friday schedule from dry off to calving. Milk yield and composition were recorded daily up to 280 d in milk. Daily dry matter intake was measured from dry off to 42 d relative to calving. Mammary biopsies were collected at dry off, -20, 2, and 20 d relative to calving from a subset of cows (HT, n=7; CL, n=7). Labeling with Ki67 antigen and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling were used to evaluate mammary cell proliferation and apoptosis, respectively. The average temperature-humidity index during the dry period was 76.6 and not different between treatments. Heat-stressed cows had higher rectal temperatures in the morning (38.8 vs. 38.6°C) and afternoon (39.4 vs. 39.0°C), greater respiration rates (78.4 vs. 45.6 breath/min), and decreased dry matter intake (8.9 vs. 10.6 kg/d) when dry compared with CL cows. Relative to HT cows, CL cows had greater milk production (28.9 vs. 33.9 kg/d), lower milk protein concentration (3.01 vs. 2.87%), and tended to have lower somatic cell score (3.35 vs. 2.94) through 280 d in milk. Heat stress during the dry period decreased mammary cell proliferation rate (1.0 vs. 3.3%) at -20 d relative to calving compared with CL cows. Mammary cell apoptosis was not affected by prepartum heat stress. We conclude that heat stress during the dry period compromises mammary gland development before parturition, which decreases milk yield in the next lactation.

Heat stress abatement during the dry period influences metabolic gene expression and improves immune status in the transition period of dairy cows.

Heat stress (HT) and photoperiod affect milk production and immune status of dairy cows. The objective was to evaluate the effects of HT abatement prepartum under controlled photoperiod on hepatic metabolic gene expression and cellular immune function of periparturient Holstein cows (n=21). Cows were dried off 46 d before expected calving date and assigned to treatments by mature equivalent milk production. The treatments were 1) HT and 2) cooling (CL), both imposed during a photoperiod of 14L:10D. Rectal temperature was measured twice daily, whereas respiration rate was measured 3 times/wk at 1500 h during the entire dry period. After calving, cows were housed in a freestall barn with cooling, and milk yield was recorded daily up to 140 d in milk. Liver samples were taken at dry off, -20, 2, and 20 d relative to calving by biopsy. Under a similar schedule, neutrophil function was determined in blood of cows on HT (n=12) and CL (n=9). Blood samples were taken on -46, -32, -18, 0, 14, 28, and 42 d relative to calving for measurement of metabolites and were collected twice daily from -7 to 2 d relative to calving for prolactin (PRL) analysis. The HT cows had greater concentrations of PRL at 0 d relative to calving (150 vs. 93; SEM=11 ng/mL) and had higher afternoon rectal temperatures (39.4 vs. 39.0; SEM=0.04°C) and elevated respiration rates (78 vs. 56; SEM=2 breaths/min) during the prepartum period compared with CL cows. Relative to HT cows, CL cows had greater hepatic expression of PRL-R, SOCS-3, and CAV-1 mRNA. Neutrophil oxidative burst was greater in CL cows relative to HT cows at 2 d (61 vs. 42; SEM=6%) and at 20 d (62 vs. 49; SEM=5%) relative to calving, and phagocytosis was greater in CL cows at 20 d (47 vs. 33; SEM=4%) relative to calving compared with HT cows. Humoral response, as measured by IgG secretion against ovalbumin challenge, was greater for CL cows at -32 d (0.44 vs. 0.33; SEM=0.05 OD) and -21 d (0.60 vs. 0.50±0.04 OD) relative to calving compared with HT cows. These results suggest that HT abatement during the dry period improved innate and acquired immune status as measured by neutrophil function and immunoglobulin secretion against ovalbumin challenge, and altered hepatic gene expression related to PRL signaling in the periparturient period or subsequent lactation.

Short communication: Effect of estrogen supplemented at dry-off on temporal changes in concentrations of lactose in blood plasma of Holstein cows.

The objective was to determine the effect of supplemental estrogen (estradiol cypionate, ECP) at dry-off on temporal changes in concentrations of lactose in blood plasma of Holstein cows as an indicator of rate of mammary involution. Thirty-two Holstein cows (8/group) were assigned randomly to 4 treatment groups: 30-d dry, 30-d dry + ECP, 60-d dry, and 60-d dry + ECP. A single injection (7.5 mL) of cottonseed oil (30- and 60-d dry) or ECP (15 mg) in oil (30- and 60-d dry + ECP) was administered intramuscularly at dry-off. Blood samples were collected from the coccygeal vein of all cows 24 h before dry-off and at dry-off, and then 8 samples were collected throughout the subsequent 48 h to monitor concentrations of lactose in blood plasma. No significant effects of ECP on the overall mean concentrations of lactose were detected. Concentrations of lactose increased and were greatest in blood collected 20 h (520.4 +/- 54.1, 268.1 +/- 48.2, 345.0 +/- 52.3, 418.4 +/- 49.8 microM, for the 4 treatment groups respective to the order listed above) after supplemental ECP and final milk removal. At 40 h, concentrations approached those observed 24 h before dry-off (140.5 +/- 52.1, 57.6 +/- 47.1, 90.1 +/- 51.4, 61.2 +/- 48.4 microM, respectively). Concentrations of lactose at 20 h were positively correlated with milk yield of cows at dry-off. Similar temporal profiles of lactose in blood plasma of cows supplemented or not with ECP indicated that ECP at dry-off did not markedly alter the course of tight junction leakage that typically occurs in mammary epithelial tissue during progressive early involution when milk removal is discontinued.

Supplementing Holstein cows with low doses of bovine somatotropin prepartum and postpartum reduces calving-related diseases.

The objective of this study was to evaluate whether supplementing Holstein cows with bovine somatotropin (bST; 142.8 mg/14 d), beginning at 21 d (+/-3 d) before expected calving and continuing through 42 d in milk (+/-3 d), affected the incidence rates of retained fetal membranes (RFM), metritis (MET), clinical mastitis (MAS), digestive problems (DIG), ketosis (KET), milk fever (MF), displaced abomasum (DA, left or right), lameness (LAM), or number of sick cows during the first 60 d in milk. Data for multiparous Holstein cows from 3 separate trials were merged for analyses (n = 437). Cows in the bST-supplemented group (n = 162) received biweekly subcutaneous injections of Posilac, whereas control cows (n = 166) and a group of cohorts (n = 109) were not supplemented. Incidences of disease were collected from the herd health records. Across all treatment groups, the incidence rates (number of diseased cows divided by the total number of cows) for RFM, MET, MAS, DIG, KET, MF, DA, and LAM were 8.47, 18.31, 16.02, 4.35, 4.35, 3.66, 3.20, and 3.66%, respectively. The incidence rates of RFM, MET, MAS, DIG, KET, MF, DA, and LAM for cows in the bST-supplemented, control, and cohort groups were 6.79, 7.83, and 11.93%; 16.05, 7.47, and 22.94%; 10.49, 18.07, and 21.10%; 1.23, 5.42, and 7.34%; 1.23, 6.02, and 6.42%; 2.47, 4.22, and 4.59%; 2.47, 3.61, and 3.67%; and 3.70, 3.61, and 3.67%, respectively. The percentages of sick cows (number of cows having one or more cases of disease divided by the total number of cows) in the bST-supplemented, control, and cohort groups were 33.95, 43.37, and 49.54%, respectively. Significant chi-squared values were detected between the bST-supplemented and control groups for MAS, DIG, and KET, with a greater number of healthy cows in the bST-supplemented group. No differences in incidences of diseases or sick cows were detected between the control and cohort groups. Results indicated that a low dose of bST supplemented to Holstein cows for 3 wk prepartum through 60 d in milk reduced the incidences of some calving-related diseases compared with nonsupplemented controls or cohorts. Importantly, no negative effects of bST supplementation on postpartum calving diseases were detected compared with nonsupplemented cows.

Milk production from Holstein half udders after concurrent thirty- and seventy-day dry periods.

The objective of this study was to use a within-cow, half-udder model to compare the effect of cessation of milk removal from mammary quarters within respective half udders at either 30 or 70 d before expected calving date (ECD) on the ability of the half udders to subsequently produce milk. Pregnant Holstein cows were assigned to control (n = 14) or treatment (TRT, n = 26) groups. All mammary quarters in the udder of cows in the control group had 70-d (68 +/- 9 d) dry periods, whereas in each cow of the TRT group, 1 randomly selected half udder was dried at 70 d before ECD and the other half udder continued to be milked twice daily until dried at 30 d before ECD. From 80 through 70 d before ECD, amounts of milk produced by the left and right half udders of cows in the TRT group were measured at the first-shift milking. No differences were detected in the actual or relative amounts of milk produced by the left (3.46 +/- 0.2 kg; 48.8 +/- 1.0%) and the right (3.63 +/- 0.2 kg; 51.2 +/- 1.0%) half udders. Furthermore, the actual and relative amounts of milk produced by the half udders (n = 12 left, 14 right) subsequently dry for 67 +/- 7 d (3.56 +/- 0.2 kg; 50.2 +/- 1.0%) and the half udders (n = 14 left, 12 right) subsequently dry for 27 +/- 7 d (3.54 +/- 0.2 kg; 49.8 +/- 1.0%) did not differ before they were dried. However, from 3 to 100 d of the subsequent lactation, the 30-d dry half udders produced 18.9% less milk than the 70-d dry half udders (16.3 vs. 20.1 +/- 1.0 kg/d). In addition, relative amounts of total-udder milk produced by the 30- and 70-d dry half udders in the same cow differed (44.9 vs. 55.1 +/- 0.2%, respectively). Cows in the control group produced more milk than cows in the TRT group through 80 DIM (39.5 vs. 35.2 +/- 0.6 kg/d), but not from 3 through 150 DIM (39.0 vs. 36.2 +/- 1.6 kg/d). Thus, half udders that produced the same actual and relative amounts of milk before being dried did not do so when given a 30-d dry period instead of a 70-d dry period. When compared with the pre-dry value (49.8%), the relative contribution of half udders dry for 30 d to the total milk yield during the first 100 DIM was decreased by 9.8%.

Low doses of bovine somatotropin during the transition period and early lactation improves milk yield, efficiency of production, and other physiological responses of Holstein cows.

The objectives of this experiment were to determine whether low doses of bovine somatotropin (bST) during the transition period and early lactation period improved dry matter intake (DMI), body weight (BW), or body condition score (BCS); provoked positive changes in concentrations of somatotropin, insulin, insulin-like growth factor-I (IGF-I), glucose, nonesterified fatty acids, and Ca; or improved milk yield (MY) response without obvious adverse effects on health status. Eighty-four multiparous Holstein cows completed treatments arranged in a 2 x 3 x 2 factorial design that included prepartum and postpartum bST, dry period (30 d dry, 30 d dry + estradiol cypionate, and 60 d dry), and prepartum anionic or cationic diets. Biweekly injections of bST began at 21 +/- 3 d before expected calving date through 42 +/- 2 d postpartum (control = 0 vs. bST = 10.2 mg of bST/d; POSILAC). At 56 +/- 2 d in milk, all cows were injected with a full dose of bST (500 mg of bST/14 d; POSILAC). During the prepartum period and during the first 28 d postpartum, no differences in mean BW, BCS, or DMI were detected between the bST treatment group and the control group. During the first 10 wk of lactation, cows in the bST treatment group had greater mean MY and 3.5% fat-corrected milk yield and lower SCC than did cows in the control group. When cows received a full dose of bST, an increase in milk production through wk 21 was maintained better by cows in the bST group. Mean concentrations of somatotropin, IGF-I, and insulin differed during the overall prepartum period (d -21 to -1). During the postpartum period (d 1 to 28), cows in the bST group had greater mean concentrations of somatotropin and IGF-I in plasma. Concentrations of Ca around calving did not differ because of bST treatment. Results suggest that changes in concentrations of blood measures provoked by injections of bST during the transition period and early lactation period resulted in improved metabolic status and production of the cows without apparent positive or negative effects on calving or health.

Responses of Holstein cows to a low dose of somatotropin (bST) prepartum and postpartum.

Objectives were to evaluate the effects of a low dose of bovine somatotropin (bST) injected prepartum and postpartum on body condition score (BCS), body weight (BW), and milk yield (MY) in cows as well as somatotropin insulin, insulin-like growth factor-I (IGF-I), glucose, and nonesterified fatty acids (NEFA) in plasma. Holstein cows nearing second or later parities were assigned randomly to control (CON = 98) or bST-treated (TRT = 95) groups. Biweekly injections of bST began 21 +/- 3 d before expected calving and continued through 42 d postpartum (CON vs. TRT; 0 vs. 10.2 mg of bST/ d). From 42 to 100 d postpartum, no cows received bST. During yr 1, somatotropin, IGF-I, insulin, NEFA, and glucose were measured in plasma samples from 82 cows. During yr 2, effects of bST on BCS and BW of 111 cows were evaluated, but no blood samples were collected. Milk yields through 100 d of all 193 cows were analyzed. Prepartum treatment with bST resulted in greater prepartum plasma concentrations of somatotropin, insulin, and numerically greater NEFA but did not affect glucose or IGF-I. Postpartum bST increased mean plasma concentrations of somatotropin and NEFA, but not INS, IGF-I, or glucose. Mean BCS of cows did not differ prepartum, around parturition, or postpartum. Although mean BW did not differ prepartum or around calving, cows receiving bST maintained greater BW postpartum. Cows receiving bST tended to have higher MY (6.6%) in the first 60 d of lactation, but differences did not persist through 100 d, including approximately 40 d when no cows received bST. Number of cows that were culled due to health (CON = 3 vs. TRT = 2) or died (CON = 3 vs. TRT = 1) were not affected by treatment. Low doses of bST in the transition period resulted in higher postpartum BW, quicker recovery of body condition during lactation, and significantly more milk during treatment.

Milk production and feed intake of Holstein cows given short (30-d) or normal (60-d) dry periods.

Eighty-four Holstein cows were utilized to evaluate effects of dry period (60 d vs. 30 d), with or without estradiol cypionate (ECP) injections to accelerate mammary involution, on prepartum and postpartum dry matter intake (DMI), body weight (BW), body condition score (BCS), and subsequent milk yield (MY). Treatments were arranged in a 3 x 2 x 2 factorial design that included dry period (30 d dry, 30 d dry + ECP, and 60 d dry), prepartum and postpartum bovine somatotropin (bST; 10.2 mg/d), and prepartum anionic or cationic diets. To accelerate mammary involution, ECP (15 mg) was injected intramuscularly at dry-off. No interaction of bST or prepartum diet with dry period length was detected on BW, BCS, or MY. No significant effects of dry period length on prepartum DMI, BW, or BCS were detected. Cows with shorter dry periods maintained postpartum BCS better and tended to have greater DMI immediately postpartum. Mean daily yields of milk for dry period groups did not differ during overall lactation period (1 to 21 wk). Injection of ECP at the onset of the 30-d dry period did not affect MY. No significant differences due to dry period length were detected for milk, 3.5% FCM, or SCM yields during first 10 wk of lactation. Data indicated that a short dry period protocol can be used as a management tool with no loss in the subsequent milk production of dairy cows.

Milk plasmin during bovine mammary involution that has been accelerated by estrogen.

The purpose of this study was to evaluate whether the plasminogen and plasmin system within bovine mammary secretions was influenced by an estrogen treatment that was used to accelerate mammary tissue involution. Holstein cows were injected with 4 ml of ethanol excipient (n = 21) or 15 mg of estradiol-17 beta (n = 23) on each of the 4 d that preceded final milk removal. Dates of final milk removal (d 0) were designated as 60 d prior to expected dates of calving. Each mammary quarter was sampled once to collect secretions that corresponded to d 0, 3, 11, and 25 or d 1, 7, 18, and 30 of the dry period. Concentrations of plasminogen, plasmin, and somatic cells in secretions increased earlier for treated cows than for control cows. The ratio of plasminogen to plasmin in secretions decreased earlier for treated cows than for control cows. These responses support the suggestion that the plasminogen and plasmin system is involved in the involution of bovine mammary tissue. Estrogen treatment increased the activation of plasminogen, which was evidenced by a precipitous decrease in the ratio of plasminogen to plasmin that occurred as concentrations of plasminogen and plasmin increased. The activation of plasminogen likely contributed to the increased rate of mammary tissue involution that was effected by exogenous estrogen. Endogenous estrogen secreted by the developing fetal and placental unit might mediate, in part, the gradual involution that occurs during lactation.

Estrogen administered at final milk removal accelerates involution of bovine mammary gland.

To evaluate whether estrogen hastened involution of mammary tissue, Holstein cows were injected with 4 ml of ethanol excipient (n = 21) or 15 mg of estradiol-17 beta (n = 23) on each of the 4 d that preceded final milk removal. Dates of final milk removal (d 0) were designated as 60 d prior to expected dates of calving. Milk volumes were recorded, and samples were collected prior to the first and fourth injections. During the dry period, each mammary quarter within the cow was sampled once to collect secretions on dates that corresponded to d 0, 3, 11, and 25 or 1, 7, 18, and 30 of the dry period. Milk synthesis and secretion declined abruptly because of treatment. The decreased concentrations of alpha-lactalbumin, lactose, citrate, and potassium in secretions of controls, as well as the increased somatic cells, protein, lactoferrin, and sodium, occurred earlier in secretions from treated cows. These shifts of approximately 6 d, relative to days dry, suggested that exogenous estradiol increased the involution rate of mammary tissue.

Effect of pregnancy, milk yield, and somatic cell count on bovine milk fat hydrolysis.

During 12 mo, 1818 milk samples were collected from Holsteins and Jerseys (n = 261) to evaluate effects of advancing lactation and pregnancy on milk fat hydrolysis. Aliquots, cooled immediately and stored 48 h at 4 degrees C, were analyzed for free fatty acid content. Holsteins had higher acid degree values than Jerseys (.90 vs. .62). No difference in values was detected between alternate a.m. (.74) and p.m. (.76) sampling times. Repeatability of acid degree values from lactation to lactation was low (.22). Days in milk, days pregnant, and milk yield had curvilinear effects on acid degree values, whereas SCC effects were linear. Estimated acid degree value at 335 d in milk (average dry-off) was lowered from .80 to .63 when adjusted for days pregnant and to .48 when adjusted also for milk yield. These responses agree with the increased acid degree values associated with two late lactation events: increasing day pregnant and decreasing milk yield. Estrogen secreted by the developing fetal-placental unit could mediate changes in milk composition that promote milk fat hydrolysis.