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.

The objectives were to characterize the prevalence of periparturient diseases and their effects on reproductive performance of dairy cows in seasonal grazing farms. A total of 957 multiparous cows in 2 farms (555 in farm A and 402 in farm B) were evaluated and diseases characterized. At calving, dystocia, twin birth, stillbirth, and retained fetal membranes were recorded and grouped as calving problems. On d 7±3 and 14±3 postpartum, cows were evaluated for metritis and on d 28±3 for clinical endometritis based on scoring of the vaginal discharge. From parturition to 30 d after artificial insemination (AI), prevalence of mastitis, lameness, and digestive and respiratory problems were recorded. For subclinical diseases, diagnosis was based on blood samples collected from 771 cows and analyzed for concentrations of Ca, nonesterified fatty acids (NEFA), and β-hydroxybutyrate. Cows were considered as having elevated NEFA concentration if the concentration was ≥0.70 mM, subclinical ketosis if the β-hydroxybutyrate concentration was ≥0.96 mM, and subclinical hypocalcemia if the Ca concentration was ≤2.14 mM. Ovaries were scanned on d 35±3 and 49±3 postpartum for determination of estrous cyclicity. All cows were enrolled in a timed AI program and inseminated on the first day of the breeding season: on average, 86 d postpartum. Overall, 37.5% (359/957) of the cows presented at least 1 clinical disease and 59.0% (455/771) had at least 1 subclinical health problem. Prevalence of individual diseases was 8.5% for calving problems, 5.3% for metritis, 15.0% for clinical endometritis, 13.4% for subclinical endometritis, 15.3% for mastitis, 2.5% for respiratory problems, 4.0% for digestive problems, 3.2% for lameness, 20.0% for elevated NEFA concentration, 35.4% for subclinical ketosis, and 43.3% for subclinical hypocalcemia. Clinical and subclinical diseases had additive negative effects on reproduction, delaying resumption of estrous cyclicity and reducing pregnancy per AI (P/AI). Occurrence of multiple diseases further reduced reproductive efficiency compared with a single disease. Individually, subclinical hypocalcemia, elevated NEFA concentration, metritis, and respiratory and digestive problems reduced estrous cyclicity by d 49 postpartum. Elevated NEFA concentration, calving problem, metritis, clinical and subclinical endometritis, and digestive problems reduced P/AI on d 65 after AI. Moreover, calving problems and clinical endometritis increased the risk of pregnancy loss between gestation d 30 and 65. Serum concentrations of Ca and NEFA were negatively correlated, and both were associated with prevalence of uterine diseases. In conclusion, periparturient diseases were highly prevalent in seasonally calving grazing dairies and affected cows had delayed resumption of estrous cyclicity, reduced P/AI, and increased risk of pregnancy loss.

Calves born to cows exposed to heat stress during late gestation (i.e., the dry period) have lower birth weight and weaning weight and compromised passive immune transfer compared with those born to dams that are cooled. However, it is unknown if heat stress in utero has carryover effects after weaning. The objective was to evaluate the effect of heat stress (HT) or cooling (CL) in late gestation dairy cows on the survival, growth, fertility, and milk production in the first lactation of their calves. Data of animals obtained from previous experiments conducted during 5 consecutive summers in Florida were pooled and analyzed. Cows were dried off 46d before expected calving and randomly assigned to 1 of 2 treatments, HT or CL. Cooled cows were housed with sprinklers, fans, and shade, whereas only shade was provided to HT cows. Within 4h of birth, 3.8 L of colostrum was fed to calves from both groups of cows. All calves were managed in the same manner and weaned at 49d of age. Birth weight and survival of 146 calves (HT=74; CL=72) were analyzed. Additionally, body weight, growth rate, fertility, and milk production in the first lactation from 72 heifers (HT=34; CL=38) were analyzed. As expected, HT calves were lighter (means ± SEM; 39.1±0.7 vs. 44.8±0.7kg) at birth than CL calves. Cooled heifers were heavier up to 1yr of age, but had similar total weight gain (means ± SEM; 305.8±6.3 vs. 299.1±6.3kg, respectively) compared with HT heifers. No effect of treatment was observed on age at first insemination (AI) and age at first parturition. Compared with CL heifers, HT heifers had a greater number of services per pregnancy confirmed at d 30 after AI, but no treatment effect was observed on number of services per pregnancy confirmed at d 50 after AI. A greater percentage of CL heifers reached first lactation compared with HT heifers (85.4 vs. 65.9%). Moreover, HT heifers produced less milk up to 35wk of the first lactation compared with CL heifers (means ± SEM; 26.8±1.7 vs. 31.9±1.7kg/d), and no difference in body weight during lactation was observed (means ± SEM; HT: 568.4±14.3kg; CL: 566.5±14.3kg). These data suggest that heat stress during the last 6wk of gestation induces a phenotype that negatively affects survival and milk production up to and through the first lactation of offspring.

Calves born to cows exposed to heat stress during the dry period and fed their dams' colostrum have compromised passive and cell-mediated immunity compared with calves born to cows cooled during heat stress. However, it is unknown if this compromised immune response is caused by calf or colostrum intrinsic factors. Two studies were designed to elucidate the effects of colostrum from those innate to the calf. The objective of the first study was to evaluate the effect of maternal heat stress during the dry period on calf-specific factors related to immune response and growth performance. Cows were dried off 46 d before expected calving and randomly assigned to 1 of 2 treatments: heat stress (HT; n=18) or cooling (CL; n=18). Cows of the CL group were housed with sprinklers, fans and shade, whereas cows of HT group had only shade. After calving, the cows were milked and their colostrum was frozen for the subsequent study. Colostrum from cows exposed to a thermoneutral environment during the dry period was pooled and stored frozen (-20 °C). Within 4h of birth, 3.8L of the pooled colostrum from thermoneutral cows was fed to calves born to both HT and CL cows. Day of birth was considered study d 0. All calves were exposed to the same management and weaned at d 49. Blood samples were collected before colostrum feeding, 24h after birth and twice weekly up to d 28. Total serum IgG concentrations were determined. Body weight was recorded at birth and at d 15, 30, 45, and 60. Relative to CL calves, HT calves were lighter at birth (38.3 vs. 43.1 kg), but no difference in weight gain was observed at d 60. Additionally, HT calves had lower apparent efficiency of IgG absorption (26.0 vs. 30.2%), but no differences were observed for total IgG concentration. The objective of the second study was to evaluate the isolated effect of the colostrum from HT cows on calf immune response and growth performance. The experimental design was identical to the first study, but all calves were born to cows under thermoneutral conditions during the dry period. At birth, calves were blocked by sex and birth weight and then randomly assigned to 1 of 2 treatments, which meant they received pooled colostrum from HT cows or CL cows. No treatment effect was observed on passive immune transfer or on postnatal growth. Thus, heat stress during the last 6 wk of gestation negatively affects the ability of the calf to acquire passive immunity, regardless of colostrum source.

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.