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Prepubertal Friesian heifer calves (n = 24, initial BW = 195 ± 5 kg) were assigned to a 2 × 2 factorial block design and used to evaluate the effects of daily GH treatment (0 or 15 mg/d) at either a low or a high feeding level in a 5-wk treatment period on endocrine measurements, hormone receptors, muscle growth, and overall performance. In the pretreatment period, a low feeding level was employed for all calves. During the treatment period, animals at the low feeding level had free access to a roughage-based mixture, whereas animals at the high feeding level had free access to a concentrate mixture and were offered 2 kg/ d of the roughage-based mixture. Blood samples were collected weekly starting 3 wk before treatment. Longissimus (LM) and supraspinatus (SS) muscles were obtained at slaughter. Metabolizable energy intake was 81% higher, digestible CP intake was 140% higher, and ADG was 115% higher (all P < 0.001) at the high vs. low feeding level. Feed (DMI, ME, and protein) intake was not affected by GH treatment, but ADG was 18% higher (P < 0.13) in GH-treated than in control heifers at both feeding levels. Although of different magnitudes, the muscle anabolic effects of GH treatment and high vs. low feeding level were additive, and both treatments increased carcass weights (P < 0.02 and P < 0.001, respectively), LM (P < 0.05 and P < 0.001), and SS (P < 0.06 and P < 0.003). The anabolic effect of GH treatment was similar in both muscles, whereas the effect of feeding level was most pronounced in LM. Overall, GH treatment increased plasma GH, IGF-I (both P < 0.001), and IGFBP-3 (P < 0.02); however, GH treatment increased total IGF-I, free IGF-I, and IGFBP-3, and decreased IGFBP-2 mainly at the high feeding level (GH × feeding level interaction; P < 0.02, 0.01, 0.03, and 0.10, respectively). The high feeding level increased insulin, free and total IGF-I, and IGFBP-3 (all P < 0.001), but decreased GH and IGFBP-2 (both P < 0.001). High feeding increased type-1 IGF receptor density (P < 0.02), mainly in LM, in accordance with the largest anabolic response in this muscle, whereas GH treatment had no effect on type-1 IGF receptors. The results suggest that in skeletal muscle, the anabolic effects of exogenous GH are related to endocrine changes in the GH-IGF axis, whereas the effects of feeding level also seem to rely on IGF receptor density in the muscles. [ABSTRACT FROM AUTHOR]

Traditional starch-rich concentrates for milk-fed calves induces an acidotic ruminal environment even with small daily intakes. A new feeding regimen including use of low-starch concentrate was formulated and tested for impact on ruminal environment and -development in 2 to 10 wk old calves. Eight Holstein calves (48 ± 1 kg BW at birth) implanted with ruminal cannulaes (20 mm ID) at d 7 ± 1 of age were allocated to one of two feeding regimens. Calves on control treatment (CON) had free access to a barley-based concentrate (319 g starch/kg) from wk 1. Calves on alternative treatment (ALT) had no access to concentrate until wk 4 when they got free access to a low-starch concentrate (68 g starch/kg). All calves had free access to artificiallydried grass hay, and water and were fed skim-milk-based milk-replacer (4.6 L/d in wk 1 to 2, 6.4 L/d in wk 2 to 7, and 3.2 L/d in wk 7 to 8). Every wk, 8 ruminal samples/calf were collected from 0730 to 2400. There were no treatment effects on ADG (802 ± 35 g/d) or total solid feed DMI (concentrate + hay; 78 ± 4 kg). On ALT compared with CON, average ruminal pH was higher (6.39 vs. 6.04 ± 0.09, P < 0.05) and minimum ruminal pH was higher (6.14 vs. 5.57 ± 0.09, P < 0.01). A relatively large treatment x wk interaction was found for all VFA data. Especially from wk 2 to 4 the butyrate profile and the ruminal butyrate concentration was smaller (P < 0.001) for ALT (1 to 3 ± 1 mmol/L) compared with CON (6 to 9 ± 1 mmol/L). However, when concentrate was introduced to ALT calves ruminal butyrate increased to a higher (P < 0.001) level (12 to 19 ± 1 mmol/L) compared with CON (8 to 13 ± 1 mmol/L). No differences between treatments in ruminal mass, length, shape and aggregation of ruminal papillae were detected at wk 10. Our results show that it is possible to formulate rumen-friendly low-starch concentrates without compromising growth or ruminal development in milk-fed calves. [ABSTRACT FROM AUTHOR]

Eight Holstein calves (44 ± 1 kg BW at birth) implanted with ruminal cannulaes (20 mm ID) at d 7 ± 1 after birth were used to investigate the effects of milk allowance on concentrate intake and ruminal fermentation patterns. Calves were allocated to one of four treatments (3.0, 4.7, 6.4 or 8.1 L skim-milk-based milk-replacer/d; 130 g solids/L milk). All calves had free access to a barley-based starter concentrate (319 g starch/kg), artificially-dried hay, and water. Ruminal samples were collected every 2 h for 24 h at wk 2, 3, 4, and 5. Ruminal pH was measured immediately and ruminal fluid was stabilized with metaphosphoric acid for later analysis. Concentrate intake was affected by a treatment times wk interaction (P < 0.01). The smallest concentrate intake was found with 6.4 L milk/d (17 g/d in wk 2 increasing to 389 g/d in wk 5) and the greatest concentrate intake was found with 3.0 L milk/d (310 g/d in wk 2 increasing to 1,601 g/d in wk 5 [SEM = 150]). Daily gain from wk 2 to 5 (714 ± 35 g/d) was not affected (P = 0.49) by treatment. The average (5.8 ± 0.1) and the minimum (5.4 ± 0.1) ruminal pH within a sampling period were not affected (P > 0.24) by treatment or wk. Hours/d with ruminal pH below 6.2 (18 ± 2 h/d), 5.8 (14 ± 2 h/d), and 5.4 (6 ± h/d) were not affected (P > 0.18) by treatment or wk. The total VFA concentration was affected by week (P < 0.01) and increased from 71 ± 9 mmol/L in wk 2 to 133 ± 9 mmol/L in wk 5. All data for calves with concentrate intakes above 25 g/d showed no relationship between concentrate intake level and severity of ruminal environment. The implication is that starch-based concentrates in general might be harmful to the juvenile rumen of milk-fed calves and more attention should be paid to formulating rumen-friendly starter concentrates. [ABSTRACT FROM AUTHOR]