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• Increasing the amount of milk replacer (26% crude protein, 18% fat) fed increases average daily gain and efficiency of gain.
• Increasing the amount of milk replacer fed does not change the composition of body weight gain, providing that dietary protein is adequate.

INTRODUCTION

Several years ago our research group embarked on a research program to re-examine protein and energy requirements for growth of young calves. Several factors drove us to this effort. First, standards in the 1989 National Research Council Nutrient Requirements of Dairy Cattle contained many inaccuracies and did not accurately predict calf performance in the field. Second, evidence indicates that current Holstein cattle are leaner than during the time period when most of the existing research data on calf growth and body composition were collected, likely as a result of genetic selection for milk production. Leaner body composition could impact nutrient requirements for tissue growth. Third, the “correct” content of crude protein (CP) in milk replacers has been debated vigorously for years without appropriate data on effects of milk replacer composition and feeding rates on body composition. Fourth, milk replacer formulation is vastly different than 20 years ago, as today’s “all-milk” milk replacer are based on whey proteins rather than on skim milk powder that contains casein. Finally, changing paradigms in the dairy industry, including trends to larger herd size, custom heifer rearing, and “accelerated growth” programs have created new interest in efficient growth of dairy heifers.

Results of a large research project with multiple objectives are reported in this paper and the two that follow. This article reports the impact of energy intake (manipulated by feeding increasing amounts of milk replacer) on growth and body composition. It is a fundamental concept of animal growth that increasing energy intake increases rates of gain, eventually reaching the maximum achievable growth rate for the individual if other nutrients are not limiting. However, few data are available to document such effects in young dairy calves.

MATERIALS AND METHODS

Twenty male Holstein calves, purchased during the first week of life, were placed in hutches at the University of Illinois dairy unit. Calves were bedded on crushed rock without additional bedding to prevent consumption of material that might confound results on growth. Calves were fed whole milk at 10% of body weight for a 2-week adjustment period. Calves then were allotted to one of three feeding rates (10%, 14%, or 18% of body weight as reconstituted liquid) of an all-milk-protein milk replacer (26% CP, 18% fat) that was reconstituted to 12.5% solids. Calves on 10% and 14% treatments were fed twice daily, whereas calves fed at18% of body weight were fed three times daily. Calves remained on treatments for 5 weeks, with amounts fed adjusted weekly as calves grew. All calves were weighed and measured weekly. At the end of the 5-week feeding period, calves were slaughtered at the University of Illinois Meat Science Laboratory. The visceral organs were weighed, combined into a single fraction, and ground for chemical analysis. The head, hide, hooves, and tail were combined, weighed, and ground for chemical analysis. The whole carcass was weighed and ground. Contents of water, protein, fat, ash, and energy were determined in the ground fractions. Composition of an additional 8 calves from the same lot was determined after the end of the 2-week adaptation period so that changes in body composition due to treatments could be calculated. Data were subjected to analysis of variance techniques using the linear and quadratic effects of increasing feeding rate.

RESULTS

Calves fed the higher amounts of milk replacer had softer feces but otherwise were healthy. The amount of milk replacer powder consumed, average daily gain (ADG), and efficiency of gain increased linearly as feeding rate increased (Table 1). Increases in body weight were accompanied by significantly greater daily gains of body length and heart girth, while the increased wither height did not achieve statistical significance (data not shown). The final composition of the whole body showed decreasing contents of water and protein, and increasing content of fat, as feeding rate increased (Table 1). However, the composition of body weight gain was not affected (Table 1). The composition of baseline calves was 74.9% water, 17.7% protein, and 3.6% fat. Therefore, increasing fat content of the whole body as feeding rate increased reflects the effects of increasing deposition of tissue with normal amounts of fat to the very lean starting body composition. Plasma urea concentration decreased as feeding rate increased, indicating that dietary protein was in excess at the 10% feeding rate.

Table 1. Growth of male Holstein calves fed a milk replacer (26% CP) at three intakes.

¹ L = Linear effect, Q = quadratic effect, NS = nonsignificant (P > 0.20)