Growth Performance and Feed Intake Assessment of Italian Holstein Calves Fed a Hay-Based Total Mixed Ration: Preliminary Steps towards a Prediction Model

SIMPLE SUMMARY: Calves, and particularly heifers, play a crucial role in the future of any herd, making them an essential component of dairy farms. Rearing calves, especially those intended for replacement, involves a significant investment of resources and time to achieve profitability. Therefore, ensuring the optimal health and performance of calves is of the utmost importance on dairy farms. One effective approach is to provide calves with a hay-based ration, which promotes better intakes, reduces the sorting of forage and concentrates, and ultimately enhances their overall health and welfare. This study evaluates the growth parameters of calves fed on a hay-based ration, and it also proposes a preliminary prediction model that could help farmers to make informed management decisions and select the best animals for the replacement of culled cows, thereby improving the overall productivity and efficiency of the herd. ABSTRACT: The aim of this study was to evaluate the effects of a complete hay-based total mixed ration (TMR) for calves, focusing on their feed intake, animal growth performance, and fecal output, and to develop a preliminary estimation equation for solid feed intake and body weight in Holstein heifer calves. Twenty female Italian Holstein calves (37.14 ± 2.72 kg) born between February and July were studied from the day of birth until 77 days of age. From the fourth day of life, they were fed 3 L/day of pasteurized milk twice daily and supplemented with the same hay-based TMR. The data on feed intake, fecal characteristics, and growth performances were collected and showed that these calves had adequate parameters. Moreover, the data collected was used to create equations to predict body weight and solid feed intake using a mixed model. The goodness of fit of the developed equations was evaluated by coefficients of determinations (R(2)). The equation obtained shows high R(2) (0.98 for solid feed intake and 0.99 for calf weight), indicating the satisfactory precision and accuracy needed to predict female calves’ body weight and solid feed intake.