Effect of weaning on serum biochemistry and establishment of reference intervals for peri-weaning period of Holstein calves

Highlights

• Serum biochemistry reference intervals for peri-weaned calves were established.

• Calf biochemical profile changes during the peri-weaning period.

• Pre- and post-weaning reference intervals should be used for BUN, AST and BHB.

Abstract

Biochemical profiles help vet practitioners identify problems in the weaning process when major metabolical changes occur. Reference intervals (RI) are useful in this respect but have not been established for this period. The objective of this study was twofold a) to identify the effect of time relative to weaning, adjusted for age at weaning, on the biochemical profile and b) to establish relevant RIs and assess the necessity of using time-specific RIs for the pre- and post-weaning periods instead of a single RI for this time frame. Two-hundred and forty-one clinically healthy Holstein calves from 9 commercial dairy farms were blood-sampled, at -7d, 0d and +7d relative to the day of weaning (0d). Samples were analyzed to determine the concentration of serum total protein (TP), albumin (ALB), globulin (GLOB), blood urea nitrogen (BUN), cholesterol (CHOL), triglyceride (TRIG), total bilirubin (tBIL), aspartate aminotransferase (AST), γ‐glutamyl transferase (γ-GT), β-hydroxybutyrate (BHB) and non-esterified fatty acids (NEFA). The effect of time relative to weaning (TIME-W), adjusted for age at weaning and accounting for herd- and calf-level random variation, was assessed using linear mixed models. Reference intervals for total peri-weaning (PeriRI), pre-weaning (PreRI) and post-weaning (PostRI) periods were generated with the freeware Reference Value Advisor. Established RIs were visually compared with Adult cow RIs (AC). In order to test the agreement between PeriRI and PreRI/PostRI, the Cohen's kappa coefficient (κ) was used. The effect of TIME-W was significant for all parameters, except CHOL. Estimated marginal means for TP, ALB, GLOB, BUN, AST and BHB increased across TIME-W, while those of tBIL and NEFA decreased from 0d to +7d and of TRIG decreased from -7d to 0d. Total peri-weaning period RIs differ from AC for all parameters except γ-GT; PeriRI should be used for all biochemical parameters except for BUN, AST and BHB for which, PreRI and PostRI are preferable. The latter three parameters are potential candidates for assessing weaning management.

Introduction

Physiological or pathological alterations in the function of certain organs or tissues can affect animal biochemical profile (Kerr, 2002). To determine whether profiles are within the normal range, reference intervals (RIs), which are values representing a healthy population selected based on similar criteria (Favier, 2008) are used.

Calves are born with a nonfunctional and underdeveloped rumen and initially depend entirely on milk or milk replacer to meet their nutrient requirements (Khan et al., 2016). Inclusion of dry feed in calves’ diets promotes rumen development and fermentation process; feed fermented in the rumen provides liver new types of substrates to metabolize. During the peri-weaning period, the total replacement of liquid feed with solid feed, causes a major increase in hepatic activity (Baldwin et al., 2004). Due to events associated with rumen development and nutrient metabolism and as the risk of morbidity and mortality both pre- and post-weaning is high (USDA, 2009), weaning is considered a crucial period in calf's life (Baldwin et al., 2004).

A smooth transition from liquid to solid feed promotes a less stressful weaning (Weary et al., 2009); biochemical profiles help practitioners identify problems and therefore, reference intervals would be quite useful in this respect. Available information is not very instructive, due to either small sample size (Ježek et al., 2005; Mohri et al., 2007; Perez-Santos et al., 2015), differences in breed and production system (Hugi and Blum, 1997; Egli and Blum, 1998; Knowles et al., 2000) or the fact that all calves sampled originated from only one herd (Egli and Blum, 1998; Ježek et al., 2005). Moreover, details about age at weaning are lacking in some studies (Egli and Blum, 1997; Mohri et al., 2007), and while both pre- and post-weaning samplings were included in several ones, the effect of sampling time relative to weaning has never been assessed before. Biochemical reference intervals have been established by Yu et al. (2019), but only for male unweaned calves originating from one herd. Furthermore, only Perez-Santos et al. (2015) assessed the effect of calf's age on biochemical profile using linear mixed models.

The objectives of this study were: a) to identify the effect of time relative to weaning, adjusted for age at weaning, on the biochemical profile and b) to establish relevant RIs and assess the necessity of using time-specific RIs for the pre- and post-weaning periods instead of a single RI for this time frame.