Studies in protein supplementation of low-quality roughage feeds

Alawa, John Peter (1985) Studies in protein supplementation of low-quality roughage feeds. PhD thesis, University of Glasgow.

Abstract

The work described in this thesis investigates the influence of the source of supplementary protein (N x 6.25) on the nutritive value of low protein roughage feeds. Protein supplements degrade to varying degrees in the rumen and a recognition of the protein needs of the ruminant animal separate from that of the rumen micro-organisms which reside in their digestive tract implies that various protein supplements may differ in their effects on feed utilisation and productivity of animals given roughage diets low in crude protein. In Section 1 proteins differing in rate and extent of ruminal degradation were compared as supplements to straw fed to sheep and beef cows. In Experiment 1, formaldehyde-treated soya bean meal, with approximately 80% reduced ruminal degradation due to treatment, was compared with untreated soya bean meal in mixed diets of straw and concentrate (3:1 on fresh weight basis) and adult wether sheep were restricted-fed. Total diet digestibility was not affected but nitrogen digestibility was depressed while rumen ammonia-nitrogen production and blood urea levels were reduced as a result of formaldehyde treatment. In Experiment 2, involving diets similar to those fed in Experiment 1 but in a ratio (straw:concentrate) of 3:2, growing wether sheep were fed the straw portion approximately ad libitum. Total diet digestibility was also unaffected although voluntary straw intakes were marginally reduced due to formaldehyde treatment. Rumen liquor ammonia-nitrogen and blood urea were also reduced due to treatment. In both Experiments 1 and 2 there was a gradual adjustment to low dietary protein with time, indicating a nitrogen economy by the sheep. In Experiment 3 with beef cows during months 5-8 of pregnancy, urea, untreated and formaldehyde-treated soya bean meal were compared with molassed and unmolassed sugar-beet pulp and rolled barley as the main energy supplements. The overall results showed that, for the three main protein supplements, straw DM intakes were highest for urea and lowest for formaldehyde-treated soya bean meal, with untreated soya bean meal being intermediate. This apparent increase in straw intake in response to ruminal degradability of the source of supplementary protein was confirmed in a significant linear relationship between straw DM consumption and RDP intake for the twelve dietary treatments. Rolled barley promoted higher straw intakes as an energy source than sugar-beet pulp. In Experiment 4, with lactating beef cows and their calves, untreated and formaldehyde-treated soya bean meal were also fed with either molassed sugar-beet pulp or barley and straw was given ad libitum. Formaldehyde treatment did not reduce straw consumption and its effect in increasing milk yield was marginal. There was also evidence that straw consumption responded to RDP intakes although a protein x energy supplement interaction reduced the sensitivity of this relationship. For the main energy supplements, barley promoted higher intakes than molassed sugar-beet pulp. In Section 2, other less popularly used protein sources, such as brewers grains and peas, were evaluated as protein supplements, in view of the increasing costs of feed supplements. In Experiment 5, the rumen degradabilities of both wet and dry brewers grains and their effects on voluntary straw intakes were studied. In Experiment 5.1 it was found that over half of the CP contained in wet or dry brewers grains was degraded in the rumen and that drying did not affect the effective degradability of protein in brewers grains. In Experiment 5.2 beef cows in months 5-8 of pregnancy were offered straw ad libitum and either dry or wet brewers grains unsupplemented or supplemented with urea. Neither voluntary straw intake nor digestibility was affected by treatment but significant linear relationships were found between RDP intake on the one hand and rumen ammonia nitrogen production, plasma urea and straw DM consumption on the other. There was also a significant linear relationship between rumen ammonia-nitrogen production and plasma urea concentrations. In Experiment 6 the chemical composition of tropical and temperate varieties of peas was studied. One particular variety of temperate peas was further evaluated as a protein supplement by comparison with brewers grains and a combination of rolled barley and soya bean meal, with straw fed ad libitum to pregnant cows.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Animal sciences
• Date of Award: 1985
• Depositing User: Enlighten Team
• Unique ID: glathesis:1985-76569
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 14:08
• Last Modified: 19 Nov 2019 14:08
• URI: https://theses.gla.ac.uk/id/eprint/76569