Different sources of forage from tropical climate in the diet of dairy calves: effects on performance, metabolism, and behavior

Abstract

Due to its effects on the rumen development process, fiber supply is usually low in diets for dairy calves. Thus, these animals' fiber requirement is not well known, with significant variation in the recommendations. On the other hand, the supply of diets with high starch content and reduced particle size can result in a high rate of fermentation and acid production in the rumen, benefiting rumen development. Still, it can reduce ruminal pH and, consequently, the consumption of dry matter, which affects not only the development process but also the animals' performance. In this sense, the inclusion of fiber derived from forage in dairy calves' diet may be essential for the calves to overcome this challenge. This research aims to evaluate the best level of inclusion of whole plant flint corn silage in the total diet of dairy calves and the effects on performance and metabolism. Also, to elucidate the effects of different sources of forage from tropical climate on dairy calves' total diet, helping to choose the best source of forage to be used during the pre-weaned phase and transition period. For this study, two experiments will be carried out. In both experiments, the animals will be separated immediately from their mothers at birth to ensure adequate colostrum. The animals will be handled equally during the first 21 days of life, receiving 6 L/day of whole milk and will have access ad libitum to water and initial concentrate, without roughage in both experiments. At 21 days of age, the animals will be divided into randomized blocks, according to sex, date of birth, and weight at 21 days, and distributed in different treatments. In experiment 1, 45 Holstein calves will be used, distributed in three treatments, each with 15 repetitions: 1) control - meal concentrate with 25% NDF, without roughage; 2) 15% CS - the inclusion of 10% corn silage in the total diet; 3) 30% CS - the inclusion of 30% corn silage in the total diet. Fecal consumption and score will be monitored daily. Weight gain and metabolic indicators of intermediate metabolism will be assessed weekly. The rumen liquid and stool samples will be collected at weeks 6, 8, and 10 of life to evaluate the fermentative profile and pH. For experiment 2, 48 Holstein calves will be used, distributed in four treatments, each with 12 repetitions: 1) control - meal concentrate with 25% NDF, without roughage; 2) CS: meal concentrate with the inclusion of % corn silage in the total diet, according to the best result obtained from experiment 1; 3) FHQ: meal concentrate with the inclusion of 7% high-quality hay in the total diet; 4) FLQ: meal concentrate with the inclusion of 7% low-quality hay in the total diet. The evaluation of consumption, performance, fermentation profile, and intermediate metabolism will be performed as described for experiment 1. Besides, fecal samples for analysis of digestibility will be collected at weeks 8, 9, and 10 of age. The behavior will be performed at weeks 6, 8, and 10 of life, totaling 15 hours of observation. In the tenth week of life, four blocks will be randomly chosen to be slaughtered, the compartments will be weighed, and different points of the rumen will be collected for morphometric analysis. The data will be analyzed using the PROC MIXED of the SAS statistical package (version 9.0, SAS Institute Inc., Cary, NC). (AU)