Daily vaginal temperature in Girolando cows from three different genetic composition under natural heat stress

The present trial evaluated the effect of crossbred composition and Temperature and Humidity Index (THI) on vaginal temperature (VT) of Girolando dairy cows maintained under tropical pasture during warm seasons. The VT was monitored along 41 to 96 h in 615 Girolando cows with different Holstein (H) × Gir genetic composition (1/2 H = 284, 3/4 H = 248, and 7/8 H = 83) from six Brazilian farms in the summer of 2016 and 2017. VT of each cow at each hour of the day and the respective THI were averaged per hour across all monitoring days to generate an averaged value for VT and THI during 24 h. A linear mixed model with repeated measures using restricted maximum likelihood (REML) method for (co)variance components estimation procedure was employed. The final model adjusted the VT for the effects of cow, time, THI, farm, year, pregnancy status, body condition score (BCS), milk yield, genetic composition, and genetic composition*time interaction. Fixed effects were evaluated by ANOVA and tested with Tukey test in R software version 3.6.1 (R Core Team, 2019). Overall mean of VT, air temperature (AT), and THI were 39.06 ± 0.52 °C, 25.63 ± 0.40 °C, and 75.06 ± 3.96, respectively. VT had moderate positive correlation with THI (r² = 0.45, P < 0.001) and AT (r² = 0.46, P < 0.001). The VT had estimated linear increase of 0.05 °C for each THI unit increase (P < 0.001). Least square mean of VT varied among the farms (P < 0.001), pregnancy status (P < 0.001), and BCS (P < 0.05) but not for Milk yield (P > 0.05). The daily average VT was affected by genetic composition (P < 0.001) with highest temperature for 3/4 H (39.08 ± 0.06 °C a) and 7/8 H (39.09 ± 0.06 °C a) and lowest temperature for 1/2 H (38.95 ± 0.06 °C b). The difference of VT among the three crossbred groups varied in function of the time of the day, from 12:00 to 20:00 h (P < 0.001), with 3/4 Holstein and 7/8 Holstein cows reaching similar VT, above to the upper limit 39.1 °C and higher than 1/2 Holstein cows during all this period. In conclusion, Girolando cows are sensitive to heat stress in tropical condition during warm seasons. Moreover, Girolando cows with genetic composition higher than 3/4 Holstein display reduced thermoregulatory efficiency. Therefore, Girolando cows in tropical dairy farms require strategies to mitigate heat stress according to their genetic composition.

Chromium supplementation improves glucose metabolism and vaginal temperature regulation in Girolando cows under heat stress conditions in a climatic chamber

This study aimed to evaluate chromium supplementation on productive, reproductive, and metabolic parameters at lactating Girolando cows subjected to heat stress conditions in a climatic chamber. Thirty-six lactating Girolando cows were subjected to two sequential trials. In trial 1 (thermoneutral environment), the effect of chromium supplementation was evaluated (0 vs. 0.50 mg/kg of dry matter). In trial 2, the cows were fed the same diets, but they were divided into three environmental conditions: heat stress conditions in climatic chamber, fed ad libitum (HS); thermoneutral environment, fed ad libitum (TN); and thermoneutral environment, pair-fed (PF). In thermoneutral conditions, chromium supplementation did not affect productive or metabolic parameters, although supplemented cows had lower viability of oocytes (65.11 ± 0.08% vs. 76.86 ± 0.08%). During heat stress, chromium supplementation lowered plasma glucose levels (61.17 ± 1.90 vs. 67.11 ± 1.90 mg/dL), and increased the insulin:glucose ratio (0.39 ± 0.04 vs. 0.27 ± 0.04). Cows fed the control diet in the HS group had higher vaginal temperature values (39.40 ± 0.10 °C) than the cows in the TN group and PF group (38.89 ± 0.10 °C and 38.85 ± 0.11 °C, respectively). However, supplemented cows heat-stressed maintained the same vaginal temperature as cows in thermoneutral conditions. In conclusion, chromium supplementation improved glucose metabolism and prevented body temperature increases under heat stress conditions.

Milk production and composition, food consumption, and energy balance of postpartum crossbred Holstein-Gir dairy cows fed two diets of different energy levels

The objective of this study was to evaluate the production, consumption, and energy balance parameters of primiparous 3/4 and 7/8 Holstein × Gir (HG) dairy cows fed two diets of differing energy levels during the postpartum period. At the beginning of the study, 28 days prepartum, the average weight of both genetic groups was 498 ± 12 kg and body condition score (BCS) was 3.5 ± 0.05. At the end of the study, 61 days postpartum, the 3/4 HG cows had higher weight and body condition scores than the 7/8 HG (456 ± 8 and 429 ± 8 kg and 3.13 ± 0.03 and 2.94 ± 0.03 BCS for 3/4 HG and 7/8 HG, respectively). Milk from cows fed the high-energy diet had higher percentages of fat, protein, lactose, and total dry extract than cows fed the low-energy diet. Cows fed the high-energy diet had higher net energy intake (95.3 ± 1.9 vs. 88.1 ± 2.1 MJ/day) and higher energy balance (3.64 ± 2.13 vs - 6.02 ± 2.30 MJ/day). The 3/4 HG cows displayed higher energy for maintenance (33.1 ± 0.4 MJ/day) than the 7/8 HG (31.5 ± 0.5 MJ /day). In conclusion, although the primiparous 3/4 HG were heavier than the 7/8 HG and had a higher body condition score, no differences in milk produced up to 60 days postpartum were observed. The higher energy diet during the postpartum period increased energy balance, resulting in higher production of milk fat, protein, and lactose.

Anti-Müllerian hormone and antral follicle count are more effective for selecting ewes with good potential for in vivo embryo production than the presence of FecGE mutation or eCG pre-selection tests

This study aims to compare four different methods for selecting high responding sheep donors for in vivo embryo production. These methods include a pre-selection eCG test (eCG), antral follicle count (AFC), plasma anti-Müllerian hormone measurement (AMH) and genotyping for the presence of the FecG^E mutation (a polymorphism in the GDF9 gene associated with increased ovulation rate). Santa Ines ewe lambs (n = 25) underwent superovulation (SOV) with 800 IU equine chorionic gonadotropin (eCG) and the corpus luteum (CL) count was recorded by laparoscopy after eight days. At the D0_eCG, blood samples for AMH and genotyping analysis were collected. Twenty-one days after the end of the eCG test, the same animals underwent SOV with 200 mg of FSH, administered in six decreasing doses, and then naturally mated. Immediately before the beginning of the FSH protocol (D0_FSH), and at the moment of the first FSH dose (D9_FSH), the AFC was assessed. Plasma AMH was again determined at the D9_FSH. After each screening process, animals were classified as having a high (HR), or low (LR), potential of response (using specific thresholds for each method). Then, the ewes' response to SOV and embryo yield for each screening method, classified as HR or LR, were compared. Animals classified as HR by AFC (HR_AFC) and by AMH concentration (HR_AMH) at the D9_FSH, produced more viable embryos than those classified as LR_AFC and LR_AMH (HR_AFC 6.2 ± 3.2 vs LR_AFC 2.8 ± 3.0 and HR_AMH 6.6 ± 3.6 vs LR_AMH 3.0 ± 2.9). Pre-selection tests with eCG and different FecG^E genotypes, either heterozygous (+/E) or wild type (+/+), were unable to discriminate HR or LR animals. A tendency (P = 0.06) to have lower plasma AMH was observed in heterozygous FecG^E (+/E) ewes. In conclusion, both AFC and plasma AMH can be used to select donor ewes with a higher potential of response for in vivo embryo production.