Efficiency of Feed Utilization by Various Animal Species Fed Similar Rations

Influence of neonatal hypothyroidism on hepatic gene expression and lipid metabolism in adulthood

Thyroid hormones are required for normal growth and development in mammals. Congenital-neonatal hypothyroidism (CH) has a profound impact on physiology, but its specific influence in liver is less understood. Here, we studied how CH influences the liver gene expression program in adulthood. Pregnant rats were given the antithyroid drug methimazole (MMI) from GD12 until PND30 to induce CH in male offspring. Growth defects due to CH were evident as reductions in body weight and tail length from the second week of life. Once the MMI treatment was discontinued, the feed efficiency increased in CH, and this was accompanied by significant catch-up growth. On PND80, significant reductions in body mass, tail length, and circulating IGF-I levels remained in CH rats. Conversely, the mRNA levels of known GH target genes were significantly upregulated. The serum levels of thyroid hormones, cholesterol, and triglycerides showed no significant differences. In contrast, CH rats showed significant changes in the expression of hepatic genes involved in lipid metabolism, including an increased transcription of PPARα and a reduced expression of genes involved in fatty acid and cholesterol uptake, cellular sterol efflux, triglyceride assembly, bile acid synthesis, and lipogenesis. These changes were associated with a decrease of intrahepatic lipids. Finally, CH rats responded to the onset of hypothyroidism in adulthood with a reduction of serum fatty acids and hepatic cholesteryl esters and to T3 replacement with an enhanced activation of malic enzyme. In summary, we provide in vivo evidence that neonatal hypothyroidism influences the hepatic transcriptional program and tissue sensitivity to hormone treatment in adulthood. This highlights the critical role that a euthyroid state during development plays on normal liver physiology in adulthood.

The effects of pelleting various diets on intake and digestibility in sheep and cattle

1. Three groups of six castrated male cattle aged 6,18 and 36 months and three corresponding groups of sheep received in turn three diets consisting of high-quality dried grass (A), low-quality grass (B) or 60% of B with 40% barley (C). For one-half of each 6-week period the grass was eaten in the long form (L) and for the other half, it was ground and pelleted (P).

2. Pelleting increased intake by 45% in sheep, from 56·8 to 82·4 g dry matter per kg W-75 per day, but only by 11% in cattle, from 81·8 to 90·7. The increase was greater for diet B (44%) than for A (19%) or C (15%), and greater for the youngest animals (38%) than for the middle-aged (17%) or oldest (20%).

3. Dry-matter digestibility was reduced by pelleting from 67·2% to 58·6% in sheep and from 69·9% to 56·9% in cattle. The reduction was greater for diets A (71·2% to 56·1%) and B (65·7% to 54·1%) than for diet C (68·7% to 63·2%).

4. A hypothesis based on the importance of particle size of digesta leaving the rumen provides a possible explanation ofthese interactions between form of roughage on the one hand, and species and age of animal or diet composition on the other.