Effects of heat stress and β-carotene supplementation on postpartum reproductive performance in dairy cows

Abstract

EXP.1 The objectives were to analyses the potential impact of heat stress in different regions, determine the monthly distribution of calving throughout the year and to investigate environmental sources of variation of days open (DO) in first lactation cows. The climate data were obtained from from the 25 official provincial meteorological stations covering the 33 provinces included in the study. Reproductive data were obtained from the bureau of Biotechnology in Livestock Production, Department of Livestock Development, Ministry of Agriculture and Cooperatives. These data contained information from 13,548 lactation records collected from years 2004 to 2006. The lower mean temperature-humidity index was observed in December (72) and the highest mean in April (80). THI differed significantly between regions (P<0.0001), and months (P<0.0001). Significant interactions between region and month (P<0.0001) was found on THI. THI values were different among regions (P<0.0001). The highest frequencies of calving were observed in September and October (13.1-14.91%) and the lowest frequencies were observed in February (4.14-5.12%). The average DO in the first lactation cows was 151.70 days. Significant effects of MOC (P<0.0001), region (P<0.0001) were found on DO. February calving cows had longest DO (219 ± 11 days) while cows calving in October and November had a significantly shorter mean DO (133 ± 7 and 133 ± 7 days). EXP. 2 The aims of this study were 1) to investigate the effect of heat stress on the resumption of ovarian activity and plasma non-esterified fatty acids (NEFA), insulin-like growth factor-1 (IGF-1) and cortisol concentrations in post partum first lactation dairy cows, and 2) to investigate the effect of heat stress on embryonic loss in first lactation dairy cows. This study was conducted in a commercial dairy farm. There were 68 first lactation cows included in the study. The proportion of normal ovarian cyclicity in mild stress (72 ≤ THI < 78) was higher than in severe stress (78 ≤ THI < 89) group (P<0.01). The interval from calving to first ovulation, interval from calving to first AI, days open and first service conception rate were not statistically different between MS and SS. BCS and body weight were unaffected by THI classification group. Plasma concentrations of NEFA, IGF-1 and cortisol, were not different between groups. Milk production was different (P=0.03) between MS and SS. Neither the number nor the different types of embryonic mortality were affected by heat stress. EXP. 3 The objective was to invesrtigate whether a supplement of β-carotne given during the dry period is able to 1) increase blood concentrations of β-carotene postpartum 2) improve ovarian function and progesterone production 3) enhance uterine involution and uterine health 4) improve milk production and milk composition 5) modify hormone and metabolic status in cow 6) increase colostral IgG content 7) modify hormone, metabolic status and enzyme activity in the neonatal calf. Forty high producing Holstein cows were included in the experiment. The β-carotene supplement was given individually to the cows (1g/d β-carotene) started at drying-off until calving. The results showed that supplementation of β-carotne during the dry period increased blood concentrations of β-carotene in cows (P<0.0001). On day 28 postpartum the percentage of neutrophils in the BC group was lower than in the C group (cervical smear; C: 21.0 ± 3.22% vs BC: 9.7 ± 3.14%, P<0.05 and uterine smear; C: 32.0 ± 3.86% vs BC: 20.9 ± 3.76%, P<0.05). Plasma concentrations of hydroxyproline in the BC group were higher than in the C group on day 21 postpartum (BC: 20.8 ± 1.33μmol/L vs. C: 15.0 ± 1.33μmol/L; P<0.01). The dietary supplement of β-carotene during the dry period had no effect on ovarian activity, progesterone production, cervix and uterine horn diameters, milk production and milk composition, hormone and metabolic status in cow, colostral IgG content, hormone, metabolic status and enzyme activity in the neonatal calf.