Reducing protein content in the diet of growing goats: implications for nitrogen balance, intestinal nutrient digestion and absorption, and rumen microbiota

Abstract

Reducing dietary CP content is an effective approach to reduce animal nitrogen excretion and save protein feed resources. However, it is not clear how reducing dietary CP content affects the nutrient digestion and absorption in the gut of ruminants, therefore it is difficult to accurately determine how much reduction in dietary CP content is appropriate. This study was conducted to investigate the effects of reduced dietary CP content on N balance, intestinal nutrient digestion and absorption, and rumen microbiota in growing goats. To determine N balance, 18 growing wether goats (25.0 ± 0.5 kg) were randomly assigned to one of three diets: 13.0% (control), 11.5% and 10.0% CP. Another 18 growing wether goats (25.0 ± 0.5 kg) were surgically fitted with ruminal, proximate duodenal, and terminal ileal fistulae and were randomly assigned to one of the three diets to investigate intestinal amino acid (AA) absorption and rumen microbiota. The results showed that fecal and urinary N excretion of goats fed diets containing 11.5% and 10.0% CP were lower than those of goats fed the control diet (P < 0.05). When compared with goats fed the control diet, N retention was decreased and apparent N digestibility in the entire gastrointestinal tract was increased in goats fed the 10% CP diet (P < 0.05). When compared with goats fed the control diet, the duodenal flow of lysine, tryptophan and phenylalanine was decreased in goats fed the 11.5% CP diet (P < 0.05) and that of lysine, methionine, tryptophan, phenylalanine, leucine, glutamic acid, tyrosine, essential AAs (EAAs) and total AAs (TAAs) was decreased in goats fed the 10.0% CP diet (P < 0.05). When compared with goats fed the control diet, the apparent absorption of TAAs in the small intestine was increased in goats fed the 11.5% CP diet (P < 0.05) and that of isoleucine, serine, cysteine, EAAs, non-essential AAs, and TAAs in the small intestine was increased in goats fed the 10.0% CP diet (P < 0.05). When compared with goats fed the control diet, the relative richness of Bacteroidetes and Fibrobacteres was increased and that of Proteobacteria and Synergistetes was decreased in the rumen of goats fed a diet with 10.0% CP. In conclusion, reducing dietary CP content reduced N excretion and increased nutrient utilization by improving rumen fermentation, enhancing nutrient digestion and absorption, and altering rumen microbiota in growing goats.

Microbiome-metabolomics analysis of the effects of decreasing dietary crude protein content on goat rumen mictobiota and metabolites

“…In the rumen, Synergistetes is known for its capability to degrade amino acids [21]. The decreased relative abundance of Synergistetes in the rumen of goat fed a low protein diet was also reported by Zhang et al [22]. The decreased apparent digestibility of CP in the LCP group observed in our previous study [4] could be partially explained by the reduced abundances of these protein-degrading bacteria.…”

Effect of Feeding Alfalfa and Concentrate on Meat Quality and Bioactive Compounds in Korean Native Black Goat Loin during Storage at 4°C

“…Creatine is enzymatically synthesized from glycine and arginine in the kidneys and liver ( Kreider et al, 2017 ). According to previous studies, concentrate contains significantly higher glycine and arginine contents at 4.9% and 7.6%, respectively ( Zhang et al, 2020 ) compared to alfalfa at 3.7% and 5.3%, respectively ( Giner‐Chavez et al, 1997 ). We, therefore, postulated that the high glycine and arginine content in concentrate may have contributed to creatine synthesis in the loin meat from the KLA group, which was then non-enzymatically transformed into creatinine.…”

“…CoQ 10 can be endogenously synthesized by a process including the synthesis of the benzoquinone ring from tyrosine as a precursor ( Bank et al, 2011 ). Although we did not perform a complete amino acid composition analysis for alfalfa and concentrate, alfalfa contains 3.3%–4.17% tyrosine ( Brito et al, 2014 ; Giner‐Chavez et al., 1997 ; Kaldy et al, 1980 ), while concentrate for goat feed has 2.87% tyrosine ( Zhang et al, 2020 ). We, therefore, postulated that the high tyrosine content in alfalfa might be related to CoQ 10 synthesis in the loin meat of the KHA group.…”

“…According to previous research, alfalfa contains 6.1%–6.6% lysine and 1.8%–1.9% methionine ( Brito et al, 2014 ; Kaldy et al, 1980 ). Meanwhile, concentrate in goat feed contains 5.63% and 1.09%, respectively ( Zhang et al, 2020 ). We, therefore, postulated that the high lysine and methionine content in alfalfa may have contributed to the synthesis of L-carnitine in the loin meat from the KHA group.…”

Effects of different protein sources on nutrient disappearance, rumen fermentation parameters and microbiota in dual-flow continuous culture system

“…Wang et al ( 2019 ) suggested that gastrointestinal tract microbial communities influences the utilization efficiency of nitrogen in goats. Zhang et al ( 2020b ) reported that reducing dietary CP content by 3% diminished the relative richness of Bacteroidetes, which might be associated with the increasing efficiency of carbohydrate utilization in the rumen. Most previous studies have concentrated on how protein levels affect ruminal microbiota, and the influence of different plant protein sources on ruminal bacterial communities has relatively not been examined.…”