To investigate the effect of heat stress (HS) on production and metabolism of Afshari sheep, 32 intact male lambs (33.2 ± 4.5 kg) were used in a completely randomized design using 2 experimental periods. In period 1 all 32 lambs were housed in thermal neutral (TN) conditions (25.6 ± 2.6°C and a temperature-humidity index [THI] of 72.0 ± 2.6) and fed ad libitum for 8 d. In period 2 (P2; 9 d), 16 lambs were subjected to cyclical HS (29.0 to 43.0°C and a THI ≥80 for 24 h/d) and the other 16 lambs were maintained in TN conditions but pair fed (pair-fed thermal neutral [PFTN]) to the HS lambs. During each period DMI and water intake were measured daily. Respiration rate, rectal temperature, and skin temperature at the shoulder, rump, and front and rear leg were recorded at 0700 and 1400 h daily. Water intake increased (P < 0.05) during P2 in both HS and TN lambs (88 and 35%, respectively). Heat stress increased the 0700 and 1400 h surface temperature at the shoulder (3.0 and 10.6%), rump (2.7 and 12.7%), rear leg (3.1 and 13%), and front leg (3.0 and 13%) and respiratory rates (72 and 124%; P < 0.01, respectively, for 0700 and 1400 h) but only the 1400 h rectal temperature was increased (P < 0.01; 0.54°C) in HS lambs. Plasma glucose concentration decreased in P2 (P < 0.01) in both the HS and PFTN lambs. Basal insulin concentrations decreased in PFTN controls but increased in HS lambs (environment × period interaction; P < 0.05). Blood urea nitrogen concentration was not affected by environment or period, but NEFA levels were slightly elevated (P < 0.01) in both PFTN and HS lambs during P2. Interestingly, HS did not affect DMI, but ADG was reduced (36%; P < 0.01) compared to the PFTN lambs. These results indicate that the direct effects of heat (not mediated by reduced DMI) are partially responsible for reduced growth in heat-stressed lambs. Copyright © 2014. American Society of Animal Science .

To distinguish between the direct effects of heat stress (HS) and reduced DMI on metabolic and physiological variables, morphometry, and gene expression of transporters involving in ruminal VFA absorption, 16 Holstein bull calves (178.1 ± 7.55 kg of BW) were used in a randomized complete design using 2 experimental periods. In period 1 (P1), all animals were housed in thermoneutral (TN) conditions (20.7 ± 3.0°C and a temperature–humidity index [THI] of 65.2 ± 3.1) and fed ad libitum for 8 d. In period 2 (P2; 9 d), half of the calves (n = 8) were subjected to HS condition (29.9 to 41.0°C and a THI ≥ 85 for 8 h/d) and the other half (n = 8) were maintained in TN conditions but were pair fed (pair-fed thermoneutral [PFTN]) to the HS calves. Heat stress decreased DMI (20%; P < 0.01) and, by design, PFTN calves had similar reduced intakes. During P1, ADG was similar between groups (1.7 kg/d), but ADG was reduced similarly for both groups (0.14 kg/d) during P2 (P < 0.01). Compared with P1, HS calves had decreased plasma glucose levels (12.5%; P < 0.01) in P2. Basal insulin levels increased in P2 for HS calves (71%; P < 0.03), but there was no difference between periods for PFTN calves. Circulating NEFA concentrations did not differ between periods in the HS calves, but PFTN animals had increased basal NEFA levels (100%; P < 0.01). Compared with P1, HS calves had increased blood urea nitrogen concentration in P2 (P < 0.01) but blood urea nitrogen did not differ between periods in the PFTN calves. Heat stress had no measurable effect on nutrient digestibility. Rumen papillae height increased (51%; P < 0.04) in HS calves whereas papillae top width decreased (40%; P < 0.03), but there was no difference between treatments for other morphometric parameters. Gene expression of VFA transporters in rumen epithelium was not affected by thermal treatments. These results confirmed that short-term HS in the current study had no effect on diet digestibility, rumen morphology, or VFA transporters genes. Therefore, HS-induced decrease in DMI is in large part responsible for gross changes in BW in growing calves (albeit tissue composition of growth is not unknown). Copyright © 2016. American Society of Animal Science .

The current study evaluated the effects of step-down weaning implementation time on starter feed intake, growth performance, blood metabolites, and ruminal pH in dairy calves. A total of 48 Holstein dairy calves (24 male and 24 female; 3 ± 1 d old; 41.2 ± 1.8 kg of body weight) were assigned (n = 12 per treatment; 6 male and 6 female) to 4 experimental treatments in a completely randomized block design. All calves were fed 6 L/d of milk from d 3 to 10 of age, and the treatments consisted of the following: calves were offered 8 L/d of milk from d 11 to 28 of age and then 4 L/d from d 29 to 63 (Step-28; total milk offered = 326 L); calves were offered 8 L/d of milk from d 11 to 42 of age and then 4 L/d from d 43 to 63 (Step-42; total milk offered = 382 L); calves were offered 8 L/d of milk from d 11 to 56 of age and 4 L/d from d 57 to 63 (Step-56; total milk intake = 438 L); and calves were fed 8 L/d of milk from d 11 to 63 of age and abruptly weaned (control; total milk offered = 466 L). All calves were housed individually in pens and had ad libitum access to water and solid feed throughout the experiment. All calves were completely milk weaned on d 64, and their performance was measured until d 80 of age. During the experiment, the starter intake (kg/d and % of body weight) was greater in calves in the Step-28 group compared with those in the other groups. However, the total metabolizable energy intake was greater in the Step-56 calves compared with the other calves. Overall, the average daily gain (ADG), feed efficiency (ADG/dry matter intake), and ADG/total metabolizable energy intake were similar across the treatments. Circulating glucose, β-hydroxybutyrate, blood urea nitrogen, albumin, total protein, alanine aminotransferase, and aspartate aminotransferase, as well as ruminal pH, were not affected by the treatments. The implementation of step-down weaning in early life (4-6 wk of age) could stimulate solid feed intake compared with weaning at a later age with no negative effect on performance.

Recent studies have shown that cows with subclinical hypocalcemia (SCH) at 4 d in milk (DIM), regardless of their blood Ca concentration before that time point, suffer from an increased early lactation disease risk and reduced milk yield, whereas cows experiencing a transient reduction in blood Ca that regain normocalcemia by 4 DIM are at a reduced risk of disease and have greater milk yields. With a goal of improving outcomes for dyscalcemic cows with SCH at 4 DIM, our primary objective was to assess the effect of a herd-level oral Ca bolus strategy that delayed supplementation to 24 and 48 h postpartum on productive performance of multiparous Holstein cows. Our secondary objectives were to assess the effects of delayed Ca bolus supplementation on blood Ca concentration, disease incidence within 30 DIM, and pregnancy risk to first service. At calving, multiparous cows on a single commercial dairy farm in Iran were randomly assigned to 1 of 3 treatment groups: 1) control, no Ca bolus administration (CON; n = 95); 2) traditional bolus, one Ca bolus administered immediately following calving and a second Ca bolus administered 24 h after calving (TRD, n = 102); or 3) experimental bolus, one Ca bolus administered 24 h after calving with a second Ca bolus administered 48 h after calving (EXP, n = 99). Blood samples were collected at 0, 24, 48, 72, 96 h and 7 d after parturition, with sampling occurring before bolus administration for the TRD (0 and 24 h) and EXP (24 and 48 h) groups. A general linear mixed model was created to analyze the change milk yield over the first 4 monthly tests and serum Ca concentrations over 7 DIM. Given the lack of disease events diagnosed within 30 DIM, no statistical analysis was conducted for this outcome. The effect of treatment group on risk of pregnancy to first service was assessed using Poisson regression. The incidence of dyscalcemia within CON cows was 72%. We found no difference in mean monthly milk yield among treatment groups across the first 4 tests, with an average monthly production of 51.8 ± 8.8 kg/d for CON cows, 52.5 ± 8.7 kg/d for TRD cows, and 51.8 ± 8.7 kg/d for EXP cows. Mean blood Ca concentration also did not differ across 7 DIM among treatment groups and was 2.04 mmol/L (95% confidence interval [CI] = 2.00 to 2.07 mmol/L) for CON cows, 2.06 mmol/L (95% CI = 2.03 to 2.09 mmol/L) for TRD cows, and 2.09 mmol/L (95% CI = 2.05 to 2.12 mmol/L) for EXP cows. The risk of pregnancy to first service was numerically greater for CON than TRD and EXP cows but not statistically different; however, our study was underpowered for this outcome. Under the conditions of our study, our findings suggest that delaying oral Ca bolus supplementation to 24 h and 48 h postpartum has no effect on milk production across the first 4 monthly tests.

The effects of a grain source (corn grain (CG) vs. barley grain (BG)) and starter protein content (19% vs. 22% CP, dry matter basis) on growth performance, digestibility, ruminal fermentation, and blood metabolites were evaluated in Holstein dairy calves. Forty 3-day-old female calves with a starting body weight of 39.3 kg were subjected to four treatments in a completely randomized design with two by two factorial arrangements. Treatments were: (1) CG + 19% CP (CG-19CP); (2) CG + 22% CP (CG-22CP); (3) BG + 19% CP (BG-19CP); and (4) BG + 22% CP (BG-22CP). All calves were weaned at 59 days of age and remained in the study until 73 days of age. Starter and total DM intake were not affected by grain source and dietary protein content (p > 0.05). The average daily gain and feed efficiency were improved, and ruminal total short-chain fatty acid, propionate, and butyrate concentrations were increased in BG calves compared to CG calves (p < 0.05). The ruminal concentrations of ammonia nitrogen (d 71; p = 0.02) and acetate (d 35; p = 0.02) were increased in CG fed calves compared to BG. The greatest wither height (p = 0.03) and blood insulin concentration (p = 0.03) were seen in BG-22CP treatment. In conclusion, BG has marginal benefit in the height of calves when fed with diet containing 22% CP which may be recommendable in replacement heifer rearing programs.