The efficiency of utilization of metabolizable energy and apparent absorption of amino acids in sheep given spring- and autumn-harvested dried grass

Abstract

I. Three experiments wereconducted with sheep given spring-harvested dried grass (SHG) and autumn-harvested dried grass (AHG). The first was a calorimetric trial to determine the metabolizable energy (ME) content of each grass and the efficiency with which sheep utilize their extra ME intakes above the maintenance level of intake. The second examined the relative amounts of extra non-ammonia-nitrogen (NAN) and individual amino acids absorbed from the small intestine per unit extra ME intake as the level of feeding was raised from energy equilibrium (M) to approximately 1.5 M. The third was a further calorimetric trial to investigate the effect of an abomasal infusion of 30 g casein/d on the efficiency of utilization of AHG.2. The ME content of the SHG (11.8 MJ/kg dry matter (DM)) was higher than that of AHG (10.0 MJ/kg DM). The efficiency of utilization of ME for productive purposes (is. above the M level of intake; k,) was higher when given SHG (k, 0.54 between M and 2 M) than when given AHG (kf 0.43 between M and 2 M). Consideration is given to the possibility that the higher efficiency of utilization of ME in sheep given SHG may be related to the amounts of extra glucogenic amino acids absorbed from the small intestine which provide extra reducing equivalents (NADPH) and glycerol phosphate necessary for the conversion of acetate into fatty acids.

Comparative energy and protein utilization in kids and lambs

“…The theoretical k based on the protein content of the energy gain would be c. 0-50 (Theriez et al 1979;Sykes & Nicol 1984). Experimental evidence with adult animals having a protein energy content of the energy gain of 023 supports these theoretical calculations in that k t of spring harvested grass was 054 (MacRae et al 1985). The Agricultural Research Council (1980) would predict a value of 0-53 based on the metabolizability of the diet.…”

“…The amino acid-N content in NAN of abomasal and ileal digesta was calculated by multiplying NAN flow by 0-73 and 0-52, respectively (MacRae et al 1985). The apparent aminoacid-N absorption in the small intestine was derived by difference.…”

An evaluation of Panicum maximum cv. Gatton: 2. The influence of stage of maturity on diet selection, intake and rumen fermentation in sheep

“…During winter the high ratio of acetic to propionic acid for mature-stage pastures, together with a low pasture N content, could have resulted in inefficient utilization of acetic acid, which could have influenced the performance of animals in this treatment. MacRae et al (1985) reported that animals fed roughage diets of low N content may utilize acetic acid less efficiently.…”

The effect of cutting time of grass silage in primary growth and regrowth and the interactions between silage quality and concentrate level on milk production of dairy cows

“…A companion experiment using rumen evacuation technique revealed that the ruminal pools of DM, NDF and iNDF were smaller in cows consuming RG than PG silages suggesting that rumen fill was not limiting silage DM intake (Kuoppala et al, 2004). McRae et al (1985) reported greater absorption of amino acids from spring than autumn grass. An imbalance between absorbed amino acids and energy could potentially limit feed intake, but the AAT to ME ratios between the harvests in the current experiment (8.1 and 8.3 g AAT / MJ ME for PG and RG) do not support that conclusion.…”