| dc.description.abstract | Eighteen heifers being six Holstein, six Gyr and six Holstein-Gyr crossbred (F1) were used to determine energy and weight gain nutritional requirements of different genetic groups. The animals were adapted to experimental conditions for 70 days. The initial average body weight (BW) was 420 kg. The heifers were kept in a tie stall barn and fed ad libitum and individually twice a day at 8 am and 4 pm. The diet was composed of 70% of Tifton 85 (Cynodon dactylon) hay and 30% of a concentrate with corn, soybean meal, wheat meal and mineral/vitamin supplement. The diet was formulated to produce 900 grams/day of weight gain. The animals were weighted fortnightly to determinate average daily weight gain (ADG; kg) and feed conversion rate (FCR) in a period of 84 days. Simultaneously, an essay was conducted along five days to evaluate apparent digestibility using the total fecal collection procedure. The animals ingestive behaviours were assessed at the last day of the essay and spent time (minutes/day), percentual of feeding activities distribution, rumination, water intake, non-activity, standing and lying positions were determined for different genetic groups. The dry matter, nutrients and energy intake were higher (P<0.01) for Holsteins and Holstein-Gyr crossbred (F1) animals compared to Gyr animals. There were no significant differences between genetic groups for apparent digestibility of DM and nutrients. Time spent for feeding activities, rumination and chewing (minutes/kg DM; minutes/kg neutral detergent fiber NDF) were higher (P<0.01) for Gyr animals. Holstein and Holstein-Gyr crossbred animals remained lying for a longer time (P<0.05) than Gyr animals. The ADG was higher (P<0.05) for Holstein (0.950 kg) compared to Gyr (0.650 kg) and Holstein-Gyr crossbred (0.841 kg) had no significant difference to both pure breeds. The FCR was similar for all genetic groups (0.091). Nitrogen (N) intake had increased (p<0.001) with increased DM intake and conduced to higher N excretion. Nitrogen retention was higher (p<0.01) for Holstein. There were no significant differences (P<0.05) on the relation of intake N and retained N (0.45) among genetic groups. Gyr animals maintence net energy NEm was 83.94 kcal/kg BW0.75, 15% less compared to F1 animals with was 96.67 kcal/kg BW0.75, while Holstein animals required NEm of 113.24 kcal/kg BW0.75, 17% more than crossbred animals. Gain net energy requirements (NEg) were higher (P=0.05) for Gyr heifers (7.11 Mcal/kg of gained BW) comparing to Holstein heifers (3.03 Mcal/kg of gained BW), but there was no difference for H-G crossbred heifers (5.64 Mcal/kg of gained BW). There was no effect (P>0.05) of genetic group over respiratory quotients both to fed and fasting, diet metabolizability (q), on the relation between metabolizable energy (ME) and digestible energy (DE), neither over energetic balance (4.67 Mcal/day). Methane production (CH4) (g/day; % of gross energy consumption GE) was less (P<0.01) for Gyr animals. There was no difference (P>0.05) on CH4 production over ADG. There was no effect (P>0.05) of genetic group on energetic participation of diet with values expressed in Mcal/kg of DM of 4.13, 2.71, 2.28, 1.25 and 1.03 for GE, DE, ME, NEm and NEg, respectively. Gyr breed had less consumption potential comparing to Holstein and F1, but breeds were similar on FC and N and energetic balances. Gyr has the higher rumination rate with roughage diets than other two breeds, however, it spent higher period standing for feed. Gyr has less energetic spending with maintenance followed by F1, indicating that zebu cattle and zebu-crossed animals have less maintence energy requirements. Nevertheless, Gyr heifers had higher energy requirements for gain compared to Holstein due to be close to the adult weigth wherein F1 had equal NEg to pure breeds, indicating intermediary caracters of Gyr and Holstein. More research regarding nutritional energy requirements, energetic balance and methane production of dairy zebu cattle in tropical conditions are needed. | |
