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The welfare of dairy calves—Effects of ad libitum milk replacer intake on calf performance and rumen papillae development
Todd CG1, DeVries TJ2, Leslie KE1, Sargeant JM1, Anderson NG3, Millman ST4
1 Department of Population Medicine, University of Guelph
2 Department of Animal Poultry Science, University of Guelph
3 Ontario Ministry of Agriculture, Food and Rural Affairs
4 Veterinary Diagnostic and Production Animal Medicine, Iowa State University
Dairy calves have traditionally been fed milk at a rate of 8 to 10% of body weight per day, distributed over two meals. However, in recent years, there has been renewed interest in early calf nutrition and increased adoption of milk feeding strategies that allow calves to be fed higher volumes of milk or even ad libitum. Although research has shown that there are several benefits to offering calves milk ad libitum, the effects of feeding higher volumes of milk to calves on the development of digestive anatomy are unknown. The aim of this study was to examine the effects of offering milk replacer ad libitum on calf performance and rumen papillae development. Sixteen Holstein male calves were randomly assigned at birth to 1 of 4 milk feeding programs: 1) ad libitum intake of milk replacer (22% CP and 17% fat), 2) ad libitum intake of acidified milk replacer, 3) restricted intake (6 L/d) of milk replacer and 4) restricted intake of acidified milk replacer. Formic acid was used as a preservative to acidify the milk replacer to a target pH between 4.0 and 4.5. Milk replacer, starter ration and water intakes were measured daily, while body weight gain was determined weekly for each calf. One calf from each feeding program was euthanized at 28, 42, 56 and 70 d of age. A routine necropsy was completed on each calf and samples of rumen tissue were collected. Rumen wall thickness, as well as papillae length, width and density were measured. Regression models were constructed to examine the effects of feeding milk replacer ad libitum on important outcome variables. Calves fed ad libitum consumed significantly more milk replacer than milk-restricted calves (9.0 L/d vs. 5.3 L/d, SE=0.4, P<0.01). Calves fed ad libitum had delayed onset of starter consumption (hazard ratio = 12.3, SE=0.9, P<0.01) and consumed significantly less starter ration (1.0 kg vs. 3.8 kg, SE=0.4, P<0.01) compared to milk-restricted calves. During the first 4-weeks of life, calves fed ad libitum had higher body weight gain than the milk-restricted calves (26.0 kg vs. 14.3 kg, SE=2.8, P<0.05). Calves fed ad libitum had decreased rumen wall thickness, and reduced papillae length, width and density compared to milk-restricted calves. These results suggest that calves will consume higher volumes of milk than what is offered with traditional milk feeding strategies. Thus, feeding programs that allow for ad libitum or higher volumes of milk intake may mimic natural feeding patterns of these animals and negate feelings of hunger and improve calf welfare. These results also indicate, however, that ad libitum milk feeding delays the onset of starter ration consumption and rumen papillae development, which could negatively impact the welfare of calves during the weaning period. As such, it is recommended that further research be conducted to determine the optimum weaning protocol for calves that are consuming high volumes of milk.
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