Proteína asociada a la gestación (PAG) en vacas lecheras Holando y Normando y su correlación con metabolitos sanguíneos y composición de la leche

The aim of this study was to determine the secretion dynamics of the pregnancy-associated protein (PAG) during a biological cycle in dairy cattle Holstein Friesian (HF) and dual purpose Normande (N), in a pastoral-based dairy production system with little incidence of external supplements (SPBI). In order to better understand the relationship between circulating PAG levels and the nutritional/metabolic status of the animals, correlations were determined between PAG and energy balance data (EB), estimated net energy consumption (EC), live weight (LW), uterus weight (UW), body condition score (BCS), plasma metabolic parameters (urea, glucose, NEFA), milk yield (MY), Fat-and protein-corrected milk yield (FPCM) and milk solids composition (% protein, % fat, % lactose). Moreover, an exploratory mathematical model was established to explain the dynamics of PAG secretion throughout the biological cycle. The experiment was carried out at the Bernardo Rossengurtt Experimental Station of the Agronomy Faculty, Udelar. Twelve multiparous dairy cows, N (n = 6) and HF (n = 6) breeds were selected according to their conception date (07/15/2016 ± 13 days). Milk Yield (MY) was measured every two weeks, and once a month milk composition. Plasma PAG concentration was measured prepartum (day -11) and postpartum on days 24, 60, 161, 187, 227, 255, 279, 313 and 326, through the biological cycle.
The mean PAG concentration considering the entire study period was significantly affected by the genotype, being higher (P = 0.03) in the N genotype (9.04 ± 0.028 ng/ml) than HF (8.52 ± 0.028 ng/ml). The plasma concentration of PAG for both genotypes was adjusted to a polynomial model of degree 6. PAG presented a high and negative correlation (r=-0.67), highly significant (P- value, 4.04E-07) with the NEFAs. The % of lactose presented a medium-high, negative (r=-0.38) and significant (P=0.0044) correlation with the PAG. The PAG profiles of the present study showed that the Normando breed, which mobilizes body reserves in a short period compared to HF breed, have a better reproductive performance. In addition, in pastoral systems with seasonal fluctuations in forage supply, the concentration of PAG throughout gestation could be a good indicator of the nutritional status of the mother, which is directly related to the energy demand for growth and fetal development.