Prediction of starter feed intake of preweaned dairy calves and effects of rumen undegradable protein on performance and digestive characteristics of dairy holstein heifers

• Ano de defesa: 2017
• Autor(a) principal: Silva, Alex Lopes da
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Bovino - Alimentação e rações; Proteínas na nutrição animal; Rúmen; Digestibilidade; Ciências Agrárias; Zootecnia; Nutrição e Alimentação Animal
• Link de acesso: http://www.locus.ufv.br/handle/123456789/9977

This work was developed from three studies. Therefore, the objective of the first study was to identify variables that influence starter feed intake (SFI), and to develop equations to predict SFI in milk-fed dairy calves up to 64 days of age. The database was composed of individual data of 189 calves from 8 experiments, totaling 6,426 daily observations of intake. The information collected from the studies were: birth body weight (birth BW; kg), SFI (kg/day), fluid milk or milk replacer intake (MI; L/day), sex (male or female), breed (Holstein or Holstein×Gyr crossbred), and age (days). A correlation between SFI and the quantitative variables MI, birth BW, metabolic birth BW (birth BW 0.75), and age was established. Subsequently, data were graphed and based on a visual appraisal of the pattern of the data; an exponential function was chosen. The data were evaluated using a meta-analysis approach to estimate fixed and random effects of the experiments using nonlinear mixed coefficients statistical models. Cross-validation was used to estimate the accuracy and precision of the developed equations using the mean square error of prediction (MSEP), concordance correlation coefficient, which was decomposed into accuracy (Cb) and precision (ρ) parameters, and the coefficient of determination (r 2) as a proxy for precision. In addition, a bootstrap analysis was used to estimate the bias associated with each parameter of the developed equation structure. A negative correlation between SFI and MI was observed (r = –0.388), but age had a positive correlation with SFI (r =0.66). No effect of liquid feed source (milk or milk replacer) was observed in developing the equation. However, 2 equations, significantly different for all parameters, were fit to predict SFI for calves that consume less than 5 (SFI<5) or more than 5 (SFI>5) L/day of milk or milk replacer: SFI<5 = 0.1839±0.0581 ×MI×exp((-0.0040±0.0011× MI + 0.0333 ±0.0021) × (A- (6.0332 × MI + 0.8302±)))±0.35830.5092 - (0.12 × MI); CC>5 = 0.1225±0.0005 × MI × exp((-0.0015±0.0001 × MI + 0.0217±0.0006) × (A- (1.9508±0.1710 × MI + 3.5382±1.3140))) - (0.12 × MI); whereSFI<5 and SFI>5 = starter feed intake prediction for calves that consume less than 5 and more than 5 L/day of milk or milk replacer, respectively (kg/d); MI = milk or milk replacer intake (L/d) and A = age (days). These equations had high accuracy (Cb of 0.97 and 0.95, respectively) and the random errors of MSEP were 99.8 and 99.9% for SFI<5 and SFI>5 equations, respectively. Small biases were observed with the bootstrap analyses for all estimated parameters. The equations’ precision was moderate, with r 2 values of 0.61 and 0.52 and ρ values of 0.78 and 0.72 for SFI<5 and SFI>5, respectively. In conclusion, the use of milk or milk replacer as liquid feed did not affect SFI, or development of SFI over time, which increased exponentially with calf age. Starter feed intake was negatively affected by MI and, and for this reason, different equations are necessary to predict calf SFI according to MI. The second study aimed to evaluate the influence of different levels of rumen undegradable protein (RUP) on intake, performance, carcass characteristics, N balance, mammary gland development and hormonal status of Holstein heifers at different physiological stage (PS). Sixteen prepubertal (PRE) heifers with 106±7.6 kg of initial body weight and aged 4±0.46 months old, as well as, 16 pubertal (PUB) heifers with 224±7.9 kg of initial body weight and aged 12±0.45 months old were used. The experiment was carried out during 84 days following a complete randomized design, in a 4×2 factorial arrangement, with four levels of RUP in dietary protein (38, 44, 51, and 57%), and animals at two PS (prepubertal or pubertal). Between days 36 and 40 and between days 78 and 82 the animals were subjected to digestibility trials with collections of feeds, orts and spot collections of feces and urine. At days 0 (immediately before the beginning of the experiment) and 83 body ultrasound images were taken at the rib area. At days 0, 21, 42, 63 and 84 images of the mammary gland were taken via ultrasound. Finally, at days 0 and 84 blood samples were taken to estimate serum concentration of progesterone, estrogen, IGF-I and insulin. The PS affected the apparent digestibility of DM, and PRE heifers presented lower values. The PRE heifers also presented a preferential consumption for neutral detergent fiber corrected for ash and protein (NDFap) and sorting activity against CP greater than PUB heifers. The average daily gain (ADG) and N retention were affected by PS, and PRE heifers presented an ADG of 505 g/d, while PUB heifers presented an average value of 905 g/d. In addition, these variables were affected by RUP levels, where greater values were obtained for treatments with 51% of RUP. The analysis of pixels in mammary gland images pointed effects of PS, and PRE heifers presented greater pixels values. The initial and final measurements of serum progesterone demonstrated that PRE and PUB heifers kept their PS during the experiment. The IGF-I concentration was only affected by PS, and PUB heifers presented greater values. In addition, insulin was not affected by PS, but presented a tendency to be greater at treatments with 51% of RUP. In conclusion, the dietary level of 51% of RUP is responsible to increase the performance of PRE and PUB Holstein heifers. In addition, PRE heifers have lower sorting ability, what affected, negatively, their digestibility and performance. Finally, these animals are more likely to have greater fat proportion in the mammary gland, even under moderate rates of growth. The third study aimed to evaluate the influence of increasing levels of RUP on intake, total and partial digestibilities, rumen kinetics and characteristics, as well the N use of dairy Holstein heifers. Eight rumen-cannulated Holstein heifers, with an average initial body weight of 276±8.3 were used in a double 4×4 Latin Square design with four levels of RUP in the total dietary protein, as follows: 38% of RUP (38RUP); 44% of RUP (44RUP); 51% of RUP (51RUP) and 57% of RUP (57RUP). The experiment was carried out during 84 days subdivided into 4 experimental periods of 21 d (14 d for adaptation + 7 d for collections). Eight spot collections of feces, urine, ruminal content and omasal digesta were performed with 9 hours interval between each collection, as follows: on 15th d samples were collected at 0600 h and 1500 h; on 16th day samples were collected at 0000 h, 0900 h and 1800 h; on 17th d samples were collected at 0300 h, 1200 h and 2100 h. On 19th d a complete rumen evacuation was performed, 4 hours after the morning feeding and on 21st d immediately before morning feeding. Daily intake of DM, organic matter (OM), CP, NDFap and potential digestible NDFap (pdNDFap) were not affected by RUP levels. In addition, the relative intake (g/kg of body weight) of DM, CP and NDFap, as well as the ruminal outflow of DM, OM, CP, NDFap and pdNDFap were not affected by RUP levels. Total digestibility of DM, OM, CP, NDFap and pdNDFap, as well as ruminal and intestinal digestibilities of DM, OM, NDFap and pdNDFap were not affected by RUP levels. However, ruminal and intestinal digestibilities of CP presented a tendency to decrease according to RUP supply increase. Effects of RUP levels were not observed on the ingestion, passage and digestion rates, as well on the total volatile fatty acid concentration. Treatment 38RUP presented greater concentration of rumen ammonia nitrogen in relation to the other treatments. The urinary N excretion presented a tendency to decrease according to RUP supply increase. In addition, retained N presented a tendency to increase according to RUP levels and greater values were observed for treatments 51RUP and 57RUP. Microbial crude protein (CPmic) synthesis, microbial efficiency and the efficiency of use of N for microbial synthesis, decrease as the supplied RUP increases. Flow of RUP increased, while the amounts of rumen degradable protein decrease according to RUP supply increase. In addition, the flow of metabolizable protein presented a tendency to increase and greater values were observed for treatments 51RUP and 57RUP. In conclusion, the intestinal digestibility of CP is negatively affected by RUPvlevels, what is due to the reduction in the CPmic flow, which, probably, has greater intestinal digestibility than protein of feedstuffs. The urinary N excretion decrease according to RUP supply increase, what is due to the decrease in ruminal N losses as ammonia and the increase in N recycling. The reduction in the urinary N excretion allied to increases in the flow of metabolizable protein, which are promoted by increases in the flow of RUP to the small intestine, are determinant to promote increases in the retained N, which occurred for treatments 51RUP and 57RUP.