Mineral requirements for Nellore cattle and equations to predict milk yield and dry matter intake for lactating Nellore cows and suckling Nellore calves

• Ano de defesa: 2015
• Autor(a) principal: Silva, Luiz Fernando Costa e
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Bovino de corte (Nelore) - Alimentos e rações; Bezerros - Alimentos e rações; Minerais na alimentação animal; Ciências Agrárias; Zootecnia; Exigências Nutricionais dos Animais
• Link de acesso: http://www.locus.ufv.br/handle/123456789/6753

The aims of the first and second chapters were to estimate equations that predict the milk yield and dry matter intake of lactating Nellore cows and the dry matter intake of suckling Nellore calves; and to evaluate the effects of days of lactation on intake and nutrient digestibility, performance, milk composition, and microbial efficiency of Nellore cows and their calves. In the experiment I, fifteen multiparous Nellore cows were used, and the diet consisted of corn silage and concentrate. The experiment started on the day of calving, and the lactation period was considered to be from the day of calving until 210 days later. Milking was performed on the 7th and 15th days after calving, and again every 15 days. Additionally, calves were fed corn silage ad libitum and concentrate. The intake of the animals was recorded daily. Digestibility assays were performed every 28-d; fecal samples were collected individually over three consecutive days (6h00, 12h00, and 18h00), while urine samples were collected on the second day of collection. Nutrient intake decreased (P < 0.01) for cows while nutrient digestibility increased (P < 0.001) during the lactation period. An associative effect was observed between feed and milk intake and nutrient digestibility when calves started to receive concentrate and roughage, and it appears that the apparent digestibility of mixed feeds does not equal the sum of the digestibility of each separately measured component. Cows had little reduction in BW during the first 28-d period; afterwards, there was a quadratic effect on BW gain. The average daily gain of the calves increased (P < 0.001) during the lactation period. Microbial efficiency (g CP/kg TDN) did not change (P > 0.05) in either Nellore cows or their calves during the lactation period. Milk composition of Nellore cows did not change (P > 0.05) during the lactation period except for protein, which varies from 3.57 (Month 1) to 3.97% (Month 7). DMI of Nellore cows may be estimated by the following equation: DMI = 24.78 + 0.035 × week – 0.009 × week2, while milk yield (MY) can be estimated by MY = 8.761 – 0.0664 × week. DMI of the calves may be estimated by the following: DMI = 0.00289 × exp (exp(-0.5672) × (exp(-0.0773 × week)-1) / (-0.0773)) . Therefore, nutrient intake decreases for cows and increases for calves while nutrient digestibility decreases for calves and increases for cows during lactation period. Also, an associated effect between milk and solid feeds increased DM digestibility. Nellore cows produce milk with an average of 4.58% lactose, 5.61% fat, and the milk protein varies from 3.57 to 3.97% according to the lactation period. Also, we recommend the use of the equations proposed here to estimate the DMI of lactating Nellore cows and their calves. Also, the equation to predict MY is recommended since it presented with the best results for Nellore cows. The aim of the third chapter was to evaluate the effects of the reduction of Ca and P levels in diet on nutrient apparent digestibility and intake, performance, microbial efficiency, and the energy and protein requirements for growing Nellore heifers and steers. In the experiment II, fifty animals were used, of which 32 were Nellore heifers and 18 were Nellore steers. Four animals of each sex were used as baseline reference animals and were slaughtered at the beginning of the experiment. Four animals from each sex were fed at MAIN by receiving 11 g/kg BW, whereas 10 steers and 24 heifers were assigned to the ADLIB group. The ADLIB heifers were divided further into 4 groups according to dietary treatment: 1) Ca and P fed at their proposed requirements (CaPR) with a 50:50 roughage:concentrate (R:C) diet, 2) CaPR with a 70:30 R:C diet, 3) 43% of their proposed requirements for Ca and 80% of their requirements for P (CaPL) with a 50:50 R:C diet, and 4) CaPL with a 70:30 R:C diet. The ADLIB and MAIN steers were fed CaPR with a 50:50 R:C diet. Half of the ADLIB steers and heifers were slaughtered at d 50; the other ADLIB animals were slaughtered after 100 days of the feeding period, whereas all MAIN animals were slaughtered at d 100. Total feces and urine were collected from all animals for 72 h prior to slaughter. After slaughter, EBW was measured. The NEm and MEm requirements were estimated by exponentially relating heat production and metabolizable energy intake; NEg was estimated based on the EBW and EBG. The NPg was estimated based on the EBG and RE. Dry matter digestibility and the apparent absorption and retention of Ca and P were similar across Ca and P treatments. Final body weight, and consequently ADG, was higher (P < 0.05) for heifers that were receiving the high compared to the low concentrate diet, but dietary Ca and P concentration did not affect (P > 0.05) performance. The NEm and MEm requirements were 70.1 and 118 kcal/kg EBW0.75, respectively. Net protein for maintenance was 1.28 g/kg BW0.75 and NEg and NPg were estimated from the following equations: NEg = 0.053 × EBW0.75 × EBG0.6301 and NPg = 137.85 × EBG – 0.05 × RE, respectively. Under the conditions of this experiment, reducing the dietary concentrations of Ca and P had no significant impact on the intake, digestibility, or performance of growing Nellore heifers and steers. For chapters 4 and 5, data from another experiment (experiment III) was collected and added to the data of the experiment described in the third chapter (experiment II) in order to estimate the net requirements for maintenance and growth as well as the retention coefficients of 13 minerals (macro elements: Ca, P, Mg, K, Na, and S; and trace elements: Co, Cr, Cu, Fe, Mn, Se, and Zn) for Nellore cattle. The description of experiment II can be seen in the third chapter, while 37 Nellore bulls were used in experiment III. Bulls were divided into 3 groups: 1) baseline reference animals (n = 5), 2) animals fed at maintenance (MAIN, n = 4), and 3) animals with ad libitum access to feed (ADLIB, n = 28). The 28 ADLIB plus 4 MAIN animals were slaughtered at 4 different points (42, 84, 126, and 168 d, n = 8 – 7 ADLIB plus one MAIN/time point). The net requirements for maintenance and the retention coefficient were estimated by using the apparent absorption and retention data, as well as by using body composition. Equations were developed for each mineral as a function of empty BW by using an exponential model. The net requirements for growth for each mineral was determined based on the derivative of these equations. The net requirement for maintenance and the retention coefficients were 17.0 g/kg BW/d and 61% for Ca, 16.4 mg/kg BW/d and 82% for P, 33.0 mg/kg BW/d and 70% for K, 17.2 mg/kg BW/d and 98% for Mg, 8.5 mg/kg BW/d and 58% for Na, 2.5 mg/kg BW/d and 21% for S, 3.00 μg/kg BW/d and 16% for Cr, 1.30 μg/kg BW/d and 50% for Co, 0.03 μg/kg BW/d and 2% for Cu, 1,626 μg/kg BW/d and 43% for Fe, 14.2 μg/kg BW/d and 0.4% for Mn, 0.3 μg/kg BW/d and 15% for Se, and 280 μg/kg BW/d and 6% for Zn. Under the conditions of these experiments, the equations that were generated indicate that for a 300 kg Nellore cattle with 1.00 kg of ADG, the dietary requirements are 23.3 g/d for Ca, 15.4 g/d for P, 16.7 g/d for K, 5.59 g/d for Mg, 6.52 g/d for Na, 25.5 g/d for S, 48.9 mg/d for Cr, 26 mg/d for Co, 385 mg/d for Cu, 1,545 mg/d for Fe, 250 mg/d for Mn, 5.26 mg/d for Se, and 378 mg/d for Zn.