Abstract
The objective of this study was to investigate the effect of diet crude protein (CP) content and metabolisable energy (ME) intake on skeletal growth and associated parameters of growing steers prior to and during compensatory growth in weight and catch-up growth in skeletal elongation. The experiment was a factorial design with two cattle genotypes [Brahman crossbred (BX, 178 ± 6 kg) and Holstein-Friesian (HF, 230 ± 34 kg)] and three nutritional treatments; high CP content and high ME intake (HCP-HME), high CP content and low ME intake (HCP-LME) and low CP content and low ME intake (LCP-LME) with the ME intake of HCP-LME matched to that of LCP-LME. Nutritional treatments were imposed over a 103 d period (Phase 1), and after this, all steers were offered ad libitum access to the HCP-HME nutritional treatment for 100 d (Phase 2). Steers fed the high CP content treatment with a low ME intake, showed higher hip height gain (P = 0.04), larger terminal hypertrophic chondrocytes (P = 0.02) and a higher concentration of total triiodothyronine in plasma (P = 0.01) than steers with the same ME intake of the low CP content treatment. In addition, the low CP treatment resulted in significant decreases in bone volume (P = 0.03), bone surface area (P = 0.03) and the concentration of bone-specific alkaline phosphatase in plasma (P < 0.001) compared to steers fed the HCP-HME treatment. A significant interaction between genotype and nutritional treatment existed for the concentration of thyroxine (T4) in plasma where HF steers fed LCP-LME had a lower T4 concentration in plasma (P = 0.05) than BX steers. All steers with a restricted ME intake during Phase 1 demonstrated compensatory growth during Phase 2. However, HF steers fed the LCP treatment during Phase 1 showed a tendency (P = 0.07) for a greater LWG during Phase 2 without any increase in dry matter intake. Results observed at the growth plate and hip height growth suggest that catch-up growth in cattle may also be explained by the growth plate senescence hypothesis. Contrary to our initial hypothesis, the results demonstrate that greater CP intake during ME restriction does not increase compensatory gain in cattle during re-alimentation.
Highlights
Skeletal growth through passive stretching accounts for increases in muscle volume, sarcomere numbers and cross-sectional area of myofibers [1,2,3]
All steers exposed to nutritional restriction during Phase 1 exhibited compensatory and catch-up growth (i.e. Liveweight gain (LWG) and HH gain (HHG) respectively) during Phase 2 when compared to steers that were unrestricted during Phase 1 of the experiment
The greater gain in HH observed for the high CP content and low ME intake (HCP-LME) group during energy restriction was associated with greater T3 concentration in the plasma and larger terminal hypertrophic chondrocytes when compared to low CP content and low ME intake (LCP-LME)
Summary
Skeletal growth through passive stretching accounts for increases in muscle volume, sarcomere numbers and cross-sectional area of myofibers [1,2,3]. The term catch-up growth is commonly used in the medical literature [6, 7] and in some areas of animal physiology [8, 9], and will be adopted here to describe a faster skeletal growth rate of previously restricted animals when returning to a normal height-for-age. These two terms (i.e. compensatory and catch up growth) are sometimes adopted as synonymous [10,11,12] and in other instances treated as separated phenomenon’s based on the growth curves obtained after restoration of non-restrictive conditions [13]. During catch-up growth greater skeletal growth is explained by the growth plate delayed senescence hypothesis [14,15,16,17]
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