Differences of hormones involved in adipose metabolism and lactation between high and low producing Holstein cows during heat stress

摘要

Abstract The experiment was conducted to evaluate hormonal involvement in the adipose metabolism and lactation between high and low producing dairy cows in a hot environment. Forty Holstein healthy cows with a similar parity were used and assigned into high producing group (average production 41.44?±?2.25?kg/d) and low producing group (average production 29.92?±?1.02?kg/d) with 20 cows in each group. Blood samples were collected from caudal vein to determine the difference of hormones related to adipose metabolism and lactation. The highest, lowest, and average temperature humidity index (THI), recorded as 84.02, 79.35 and 81.89, respectively, indicated that cows were at the state of high heat stress. No significant differences between high and low producing groups were observed in the levels of nonestesterified fatty acid (NEFA), β-hydroxybutyrate (β-OHB), total cholesterol (TCHO), and insulin (INS) ( P >?0.05). However, the very low density lipoprotein (VLDL), apolipoprotein B100 (apoB-100), high-density lipoprotein (HDL-C) and estrogen (E₂) concentrations in high producing group were significantly higher than those of low producing group ( P ?0.05), whereas high producing group had a rise in the insulin-like growth factor-1 (IGF-1) level compared with low producing group ( P Keywords Heat stress ; High producing cows ; Low producing cows ; Lipid metabolism ; Lactation hormones prs.rt("abs_end"); 1. Introduction The appropriate ambient temperature for lactating cows ranges from 5 to 25°C, above which cows’ core body temperature begins to rise, leading to heat stress response ( Ray et?al., 1992 ). Over the past several decades, major advances in environmental cooling systems ( Ortiz et?al., 2015 ) and nutritional regulation have helped to ameliorate production losses, metabolic disorders and health problems during summer months. However, heat stress continues to be a challenge for global dairy industry ( St-Pierre et?al., 2003 ). In response to heat stress, dairy cows take metabolic adaptation measures to reduce heat load, such as elevating respiration rate (RR) and concomitantly reducing feed intake ( Havlin and Robinson, 2015 and Baumgard et?al., 2011 ). Due to decreased feed intake, decreased energy intake cannot meet milk energy output with the consequence of negative energy balance, which has traditionally been assumed to be primarily responsible for decreases in milk production. Adipose tissues have been well known as an important regulator in energy balance and body weight, and it is mobilized aiming to compensate for the deficient induced by decreased feed intake in response to heat stress ( Lanthier and Leclercq, 2014 ). Considering the rise in energy requirement of high producing dairy cows in lactation is parallel with increase in milk production, thereby aggravating negative energy balance, we hypothesized that lipolysis in high producing cows is more intense compared with low producing cows to maintain greater performance. In addition, secretions of prolactin (PRL), estrogen (E₂) and progesterone (PROG) involved in the formation of mammary gland are inhibited in summer, which would have a negative effect on the formation of acinus and ductal system, and contribute to lower milk production. Accordingly, the aim of the present study was to obtain insights into adipose metabolism characteristics and the levels of hormones associated to lactation in high and low producing cows in a hot environment by determining the concentration of factors related to lipid metabolism and lactation in plasma and providing theoretical reference for improving the performance of low producing cows in summer. 2. Materials and methods 2.1. Experimental design and animals The experiment was conducted at a farm located at Jiangsu province from 20 July to 20 August. Forty multiparous Holstein cows with similar ages, parities and lactation days were used and randomly assigned into high producing group (average production 41.44?±?2.25?kg/d) and low producing group (average production 29.92?±?1.02?kg/d) with 20 cows in each ( Table?1 ). Table?1. Experimental cows were selected by milk production, parity, day in milk (DIM). Item Milk production, kg/d Parity DIM, d High producing dairy cows 41.44?±?2.25 2 168?±?32 Low producing dairy cows 29.92?±?1.02 2 174?±?46 Full-size table Table options View in workspace Download as CSV 2.2. Diet ingredients and herd management The cows were housed in a tie stall barn. Fans and sprinklers were used to cool the barn. The cows were fed total mixed ration 3 times daily. The ingredient and chemical composition of basal diet are shown in Table?2 . The cows were milked 3 times daily (0730, 1130 and 1730?h) and the milk productions were recorded after each milking.