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High-yielding dairy cows are subjected to several challenges during the transition period, with metabolic stress and inflammatory condition contributing to the increased incidence and severity of diseases. This period is characterized by five critical events: reduction of immune competencies; negative energy balance resulting in mobilization of adipose and muscle tissue; hypocalcemia due to demand of the mammary gland for milk synthesis; a systemic inflammatory response around calving and oxidative stress. The Holstein is a breed selected for high production efficiency and in general, is today recognized as the breed with the highest milk production in the world. Selection for high production efficiency has often been associated with decreased longevity, increased culling rate and a sharp decrease in fertility in Holstein cows together with undesired side effects on animal welfare. A recent study of a genome-wide association between longevity traits and single nucleotide polymorphisms (SNPs), identified the presence of two possible quantitative trait loci (QTLs) which included genes with biological functions related to fertility, reproductive disorders, heat stress and cow welfare. Furthermore, increased inbreeding has been associated with fitness problems including enhanced risk of disease occurrence and reduced survival.
Crossbreeding is a practice that may help to increase the economic profit by improving health, fertility, longevity or milk components, through the benefits of heterosis, which reduces the likelihood of inbreeding depression by increasing heterozygosity. The main contribution of crossbreeding is the increase of efficiency of the production system due to breeds having their genetic merits in different traits so obtaining benefits of heterosis. In concert with these principles the study reported here aimed to evaluate plasma concentrations of energy, oxidative and inflammatory biomarkers of Simmental (sire) × Holstein (dam) crossbred cows, in comparison with the two parental breeds during the pre-calving and early lactation periods and to estimate the effects of heterosis for these traits.
Thirty-three cows, managed under the same conditions, 8 Simmental (SI), 9 Holstein (HO) and 16 crossbred (CR) cows were enrolled in this study. Glucose, non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB), total bilirubin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), creatine kinase (CK), total protein, albumin, creatinine and urea were determined in blood sampled at six different time points (30 and 15 days before the expected calving date, at calving and 15, 30 and 60 days after calving). Furthermore, derived reactive oxygen metabolites (d-ROMs), biological antioxidant potential (BAP), interleukin-6 (IL-6), haptoglobin (Hp) and serum amyloid A protein (SAA) were determined to evaluate inflammatory and oxidative status.
The results showed that the CR group had significantly lower average values of glucose and NEFA when compared to the HO group, significantly lower values of urea than the SI group and significantly higher values of creatinine than the HO. Furthermore, CR cows showed the lowest average value of d-ROMs with respect to SI and HO parental breeds, and the average value of haptoglobin was significantly lower in the CR and HO groups, when compared to the SI group. The heterosis effect showed the highest (positive) percentage for CK (98%) and BAP (47%) and the lowest (negative) percentage for OSi (−75%) and d-ROMs (−39%). The Simmental parental breed showed a negative percentage for glucose (−11%) and NEFA (−20%).
The results suggest a different response among the three genetic groups during the pre-calving and early lactation periods. In particular, CR and SI cows seem more adaptable regarding energy metabolism and oxidative status. Heterosis led to a positive effect on those parameters in the F1 Simmental (sire) × Holstein (dam) crossbred cows.