The investigation of interaction effects of feed bunk space and forage particle size on performance and feed consumption intensity within hours after feed delivery in Holstein female calves

Physical attributes of feeds and Feed bunk space can affect feeding behavior of replacement heifers. The distribution of particle size can affect feed intake, feeding behavior, and feed sorting. Research on adult dairy cattle has focused on preventing rumen acidosis by varying particle size, but less work has focused on rations for replacement heifers. On the other side, the trend in the dairy industry has been toward fewer but larger herds and a concurrent change toward group feeding and handling in the larger herds. Where herds are expanded within existing facilities, competition at the feed bunk could increase. Ad libitum feeding of complete feeds reduces this competition between lactating cattle. However, ad libitum feeding of replacement yearling heifers could result in wasted feed, overeating, and fatty infiltration of the mammary gland with a reduction in future production. The objective of this study was to evaluate the interaction effect of feed bunk space and forage particle size on growth and performance of Holstein female calves. This experiment was performed on 40 Holstein female calves with an average age of 8-12 months and an average weight of 295.6 ± 32.8 kg in a factorial design with four treatments, four periods and four stall, in which 10 calves were allocated to each stall. The length of each experimental period was 25 days and the calves were group fed in this experiment. The diets were isoenergetic and isonitrogenous. The only difference between diets was related to the forage particle size (alfalfa and straw). Treatments included: 1) treatment with 24 cm of feed bunk space and average forage particle size of 3 cm (24/fine); 2) treatment with 24 cm of feed bunk space and average forage particle size of 6 cm (24/coarse); 3) treatment with 48 cm of feed bunk space and average forage particle size of 3 cm (48/fine); 4) treatment with 48 cm of feed bunk space and average forage particle size of 6 cm (48/coarse). Sampling from feed and feeder was carried out at 15, 17, 19, and 21 days in each period. The dry matter intake of each stall was also carried out on days 15, 17, 19 and 21 in order to determine the intensity of feed consumption at 2, 4, 6, 8 hour after morning feed delivery, as the feed in the feed bunk was weighed and then returned to the feed bunk and the amount of feed consumed by every stall and for each calf was also calculated. To determine dry matter, collected samples was dried by placing them in an oven at 65-70 ° C for 48 hours (AOAC, 1990). Then the feed intake and intake intensity at different hours were corrected based on dry matter. Results of the current study confirmed the synchronize of feed consumption behavior in growing calves, which during the first 2 hours after feed delivery, calves consumed about 50-45% of the daily intake of dry matter. Also, about 90-80% of the dry matter was consumed within the first 8 hours after the feed delivery, and in the next 16 hours only 10-20% of the feed intake occurred. The results for the main effects showed that feed bunk space has no effect on daily gain, dry matter, and feed intake, while the forage particle size affected both of dry matter intake and feed conversion ratio (P <0.05), so that the feed conversion ratio was significantly higher for the treatments with fine forage particle size in comparison with treatments with coarse forage particle size (9.75 vs. 8.52). Also, daily dry matter intake for treatments with fine forage particle size was higher compared with the treatments with coarse forage particle size (7.93 vs. 7.65 kg/day/calf). Also, the amount of daily dry matter was higher for treatments with fine forage particles compared to treatments with coarse forage particles, but this higher consumption was not necessarily equal to higher daily gain. Also, there were not any significant differences between treatments containing fine forage particles and treatments with coarse forage particles for average daily gain. Finally,particle size in the growing Holstein female calves can be used as a means of controlling the dry matter and to economize the feed cost in this group of livestock. Considering the importance of controlling the dry matter intake of replacement calves, it can be stated that regarding the high proportions of forage to concentrate in growing female calves, forage particle size can be used as a management solution for controlling the dry matter intake and growth of this group of livestock. Therefore, supply of diets containing coarse forage particle size can help to economize the cost of replacing calves.