Endocrinología molecular, metabólica y reproductiva en vacas de leche con diferentes estrategias de alimentación en lactancia temprana

Resumen de tesis doctoral

Abstract

The aim was studied the biological mechanisms that regulate nutrient metabolism and how these mechanisms impact on productive and reproductive responses, combining different feeding strategies during early lactation. Three experiments were carried out using Holstein cows from the Experimental Station of the Faculty of Agronomy (Mario A. Cassinoni; Udelar). Exp1: grazing cows with different times and sessions of access to pasture + TMR vs. TMR ad libitum. Exp2: cows fed TMR ad libitum during early lactation, were assigned without period of adaptation to a mixed feeding system (grazing + TMR). Exp3: grazing cows under different herbage allowances (increasing amounts) + TMR vs. TMR ad libitum. During the transition period, cows lost BCS, increased concentrations of NEFA, BHB and genes related to fatty acid oxidation and ketogenesis, decreasing glucose concentrations, insulin and also insulin sensitivity. The decrease in IGF-I was accompanied by transcriptional changes characteristic of the decouple of the somatotrophic axis (decrease of mRNA GHR1A, IGF1, IGFBP3 and increase of IGFBP1, IGFBP2 IGFBP4, IGFBP5). During early postpartum, cows feed DTM ad libitum had higher concentrations of insulin and IGF-I, lower NEFA, BHB and lower abundance of ACADVL and HMGCOA mRNA than cows in mixed systems. Cows with two grazing sessions had lower concentrations of NEFA, higher BHB, leptin and adiponectin compared to cows in a grazing session. The inclusion of grazing, without a period of adaptation, in the diet of dairy cows fed TMR ad libitum during early lactation, decreased BW, BCS and milk production, increased IGF-1 concentrations, hepatic expression of mRNA IGF1, IGFBP3 and IGFBP5. Cows that had two sessions of grazing were the ones that had more compromised their reproductive performance, presenting greater hepatic expression of mRNA IGFBP6 and lower endometrial expression of mRNA ADIPOR1 and ADIPOR2. Cows fed TMR ad libitum and high herbage allowance had greater expression of mRNA IGF1, IGFBP3, IGFBP4, IGFBP5. The use high herbage allowance the good quality - taking into account the energy expenditure of the animals due to the activity of walking and grazing the beginning of lactation- had similar productive and reproductive results comparable to TMR ad libitum systems.