Body condition at calving affects responses to suckling management and flushing

Reproductive response and metabolic endocrinology in primiparous cows grazing native pasture: Doctoral thesis abstract

Abstract

This research was designed to test the hypothesis that the combination of a energy supplement during short periods (flushing) interacts with type of suckling management to improve the reproductive performance in primiparous Hereford cows with "suboptimal (<4.5)" body condition score (BCS) at calving grazing native grassland. It was hypothesized that the reproductive response to treatments was dependent on BCS at calving which is associated with a differential metabolic and endocrine profile. We conducted three experiments at EEFAS Faculty of Agronomy, UDELAR, Uruguay. During 3 consecutive years, 153 primiparous anoestrus cows were randomly assigned to one of four treatments in a 2 by 2 factorial arrangement of type of suckling-management treatments and flushing (Experiment 1). Suckling-restriction treatments started at 61±10 days postpartum (DPP) and consisted of applying nose plates to calves for 12 days (i.e. TS treatment) or 5 days of isolation of the calf from the cow followed by applying nose plates to calves for 7 days as calves were reunited with their mothers (i.e. IS treatment). Nutritional treatments (flushing vs control) started at the beginning of the breeding season, immediately after the suckling-restriction treatments were finished (73±10 days postpartum), with cows receiving or not 2 kg/day of whole-rice middling for 22 days. Cow body condition score (BCS, 1-8 visual scale) was recorded every 20 days from calving until 120 DPP and change in BCS during calving –start of the breeding season (ΔBCS) was estimated. The postpartum return (PPA) was estimated by plasma progesterone concentrations analyzed in weekly samples. Pregnant cows were determined by ultrasound 42 days after bull introduction (early pregnancy; EP) and 30 days after the end of the breeding season (total pregnancy; TP). In Experiment 2 the effect of BCS at calving (low ≤3.5 and moderate≥4) on endocrine and metabolic profiles during the transition period was investigated (n = 56). Cow BCS was registered and plasma insulin, insulin-like growth factor-I (IGF-I), and metabolites (urea, albumin, cholesterol, total protein, non-esterified fatty acids (NEFA)) were determined in plasma from –30 to +45 days postpartum (DPP). In the same year, the effects of BCS at calving, type of suckling restriction and flushing on metabolic and endocrine profiles (insulin, IGF-I, adiponectin, urea, -hydroxibutirate (BHB), and productive and reproductive responses of primiparous beef cows were investigated (Experiment 3).  Increased BCS at calving decreased PPA (b = –41 days, P < 0,002) and, in interaction with ΔBCS increased EP (P < 0.008) and TP (P < 0.003). Calf weights at weaning and average daily gain were not affected by suckling-restriction or flushing treatments. Isolated temporary suckling control reduced PPA by 11 days when compared with temporary suckling control (P < 0.004). Flushing increased EP by 40%, which was also affected by BCS at calving and was greater in cows that gained, than in those that maintained or lost BCS.  Cow BCS, NEFA, urea, and IGF-I profiles were affected (P < 0.05) by the BCS at calving and DPP interaction. The low BCS cows presented a smaller loss of BCS during the prepartum and a delayed BCS recovery during the postpartum respect moderate BCS cows. The increase in plasma NEFA was greater (P < 0.05) and started earlier during the prepartum period in the low BCS cows. Concentrations of IGF-I and insulin were greater (P < 0.05) in moderate than low BCS cows during prepartum, but did not differ between the groups after calving. No effects were observed in calf weight or milk production at +45 DPP. The type of suckling restriction did not affect any plasma parameter, but IGF-I concentrations increased while BHB decreased in all cows during suckling restriction. Cholesterol concentration was affected by flushing *day interaction (P < 0.05), while insulin and IGF-I concentrations were affected by the interaction among BCS at calving, flushing and days (P < 0.03). Flushing increased cholesterol concentration in both BCS groups at calving, while insulin and IGF-I concentrations increased during flushing only in moderate BCS cows. Adiponectin concentration remained constant in moderate and declined in low BCS groups. Suckling restriction, flushing, and BCS at calving did not affect calf weight or milk production. Moderate BCS cows had a shorter PPA (98 vs 123 DPP; P < 0.01) and EP rate (0.84 vs 0.46, P < 0.01). Total pregnancy rate was also greater in flushed and moderate cows and tended to be affected by the interaction between flushing and BCS at calving (P<0.10; flushed cows: moderate = 1 vs low = 0.5, P < 0.08; and control cows: moderate = 0.8 vs low = 0.4, P < 0.09).  The BCS at calving affected the evolution and the responses of the metabolic and endocrine profiles to treatments (suckling and flushing, reflecting a better nutritional status and plasticity to negative energy balance on moderate BCS cows. The suckling control with isolation reduced the anestrous length and flushing improved EP by 40 %. Both effects were modulated by body reserves (BCS at calving) differences in 0.5 points in BCS (scale 1-8= affected the endocrine milieu and reproductive efficiency. These results confirmed the great value of suckling restriction and flushing during post-calving and the relevance of BCS at calving as a link between energetic nutrition and metabolic and reproductive processes in primiparous beef cows grazing native grassland. The BCS at -45 DPP and the use of suckling management and flushing are powerful tools to stabilize the reproductive indicators and to avoid the detrimental effects of climate change in cattle breeding systems.