Effect of using either barley straw or alfalfa hay on intake and digestibility in growing Simmental heifers fed high-concentrate diets
The objective of this experiment was to compare the effects of using two different forage sources on intake and digestibility in growing heifers fed high-concentrate diets. Eight Simmental heifers (141 ± 15.5 d old and with an average initial BW of 147.4 ± 10.8 kg) were used in a crossover design experiment. Treatments tested were: a) total mixed ration with barley straw as forage source (BS), and b) total mixed ration with alfalfa hay as forage source (AH). Forages were coarsely chopped before their incorporation to total mixed ration. Diets were offered on an ad libitum basis, with a forage to concentrate ratio of 8 to 92, and formulated to be isocaloric (2.91 Mcal ME/kg DM) and isonitrogenous (15% CP on DM basis). The experiment was performed in two 28-d periods, and sampling was carried out in the last week of each period. Heifers were weighed before feeding on two consecutive days at the beginning and at the end of the experiment, and the first and last day of the sampling week. Feed offered and refusal samples of each heifer were collected daily for 7 d in the sampling week for DM determination and chemical analysis. Dry matter digestibility was estimated using acid-insoluble ash as an internal marker. Fecal samples were collected from the rectum at d 6 and 7 of each sampling period. Differences were analyzed by using the MIXED procedure of SAS. The model contained the fixed effects of treatment, period and their interaction, and the random effect of heifer nested within sequence. Intake of DM, CP and NDF was unaffected by treatment, being on average 6.4, 0.8 and 1.6 kg/d, respectively. Average daily gain of heifers fed BS tended to be greater than that of heifers fed AH (1.7 and 1.5, respectively; P = 0.10). Gain to feed ratio tended (P = 0.07) to be greater in heifers fed BS than AH (0.29 and 0.27, respectively). Dry matter digestibility and intake of digestible DM was unaffected by treatment, being on average 63.5 % and 4.1 kg/d, respectively. In conclusion, at 8% of incorporation, barley straw tended to result in a better performance than alfalfa hay when these forage sources were offered as total mixed ration to growing beef heifers.
Keywords: Beef Cattle, Forage Source, High Concentrate Diet