Abstract
The objective of this study was to investigate the effects of milk allowances equal to 526 g/d as moderate (MOD) versus 790 g/d of milk dry matter as high (HI), and starter diets containing 18% or 23% crude protein (CP), on growth performance, blood metabolites, and purine derivative (PD) excretion in the urine of dairy calves. A total of 52 female Holstein dairy calves (40.8 kg of body weight) were randomly assigned to the experimental diets. The treatments were (1) moderate milk and 18% CP starter diet (MOD-18CP); (2) MOD and 23% CP starter diet (MOD-23CP); (3) high milk and 18% CP starter diet (HI-18CP); and (4) HI and 23% CP starter diet (HI-23CP). Calves had free access to a starter feed and water and were weaned on d 53 but remained in the study until d 73. Urine samples were collected during the preweaning period (for 6 consecutive days between d 35 and 40) and postweaning period (for 6 consecutive days between d 65 and 70) to investigate urinary excretion of PD. Starter feed intake, β-hydroxybutyrate (BHB), and blood urea concentrations were reduced; however, average daily gain (ADG) and blood glucose levels increased in calves fed HI before weaning compared with MOD. During the preweaning period, high milk feeding increased total urinary PD excretion but decreased it after weaning. The 23CP diet resulted in higher feed intake and ADG before weaning and higher excretion of allantoin and total excretion of PD compared with the 18CP diet. The HI-23CP treatment resulted in the greatest withers and hip heights at weaning and final measurement, as well as the highest preweaning blood insulin concentrations. In terms of rumen development, MOD-23CP showed the greatest benefits based on starter intake, blood BHB concentration, and urinary excretion of PD. Based on the higher urinary excretion of PD found in HI-fed calves before weaning, it is possible that milk feeding overestimates estimated microbial yield. The results suggest that feeding starters with a higher proportion of CP may help maintain a more balanced ratio of CP to ME during high milk feeding, to avoid protein deficiency due to low starter intake. When calves are fed a high milk allowance, urine excretion of PD may be misinterpreted as a measure of estimated microbial growth and rumen development; this should be considered during calculations of estimated microbial yield in milk-fed calves.
Highlights
Several studies have recently been performed on providing replacement heifers with increased liquid feeding (MacPherson et al, 2016; Welboren et al, 2019; Berends et al, 2020)
Our results suggest that this problem is exacerbated when high milk feeding is combined with low starter crude protein (CP), which resulted in a CP:ME ratio of 50.2 g of CP to megacalories of ME for the high milk and 18% CP starter diet (HI-18% CP starter diet (18CP)) treatment
We did not find an interaction effect between the amount of milk fed and the protein content of the starter diet on starter intake and average daily gain (ADG), our results suggest that a higher protein content of the starter diet may add value by increasing the CP:ME ratio in calves fed a high level of milk, improving some growth indices (Table 3), and has the potential to raise calves with less body fat (Stamey Lanier et al, 2021), which needs to be further investigated in future studies
Summary
Several studies have recently been performed on providing replacement heifers with increased liquid feeding (MacPherson et al, 2016; Welboren et al, 2019; Berends et al, 2020). Dairy calves may benefit from feeding high volumes of milk in many ways, including increasing growth performance, reduction of nonnutritional behaviors (Silper et al, 2014), improving growth performance at weaning (Jasper and Weary, 2002; Khan et al, 2007), improving feed efficiency (FE) and welfare (De Paula Vieira et al, 2008; Rosenberger et al, 2017; Mirzaei et al, 2018). Preweaning calves fed ad libitum milk or milk replacer have been shown to have higher growth rates (823–1,100 g/d; Berends et al, 2020; Echeverry-Munera et al, 2021) than the upper ADG. Applying strategies to stimulate microbial growth and rumen development in early-weaned calves consuming high level of liquid feed appears necessary in commercial dairy farms
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