Effect of grazing systems and age on enteric methane production and performance plus grazing system effect on ruminal fermentation parameters of Nguni and Bonsmara beef cows

Abstract

Beef breeds of cattle are predominantly raised through extensive grazing and produce the highest levels of enteric methane (CH4) through ruminal fermentation. The objective of this study was to evaluate the effect of breed, grazing, and age on enteric methane production and performance of beef cows as well as effect of breed and grazing system on ruminal fermentation parameters. Two separate studies were conducted; the first study evaluated the effect of grazing system, breed, and age on ruminal enteric methane production and performance of selected beef breeds. The second study evaluated the effect of the grazing system and breed on ruminal fermentation. In the first study, two breeds (Nguni and Bonsmara) raised under two grazing systems (communal and commercial) in a random complete block design were grouped into 3 age categories. Eighty-four cows aged between 24-120 months were randomly selected and grouped by age: group A (young adult cow, n = 7, 24-48 months old), group B (adult, n = 7, 60-80 months old), and group C (old adult, n = 7, 90-120 months) in either grazing system. Data were collected on methane production per day, body condition, and weight used to estimate dry matter intake (DMI), methane per DMI, and methane per body weight. In the second study, 40 cows of the same age group, parity, and physiological status were used. Ten cows per breed (Bonsmara and Nguni) in either grazing system (communal and commercial) were used in a random complete block design. Rumen fluid collection was done by the stomach tube method. Data were collected on ruminal ammonia-nitrogen (NH3-N), pH, Temperature, volatile fatty acids (VFAs). Older animals produced higher methane per head in the order of C > B > A; (P0.05). Body condition, BW, and DMI were higher (P0.05) among breeds and grazing systems. However, total VFAs were slightly lower in communal grazing (78.87 mmol/L) than commercial grazing (89.80 mmol/L). Acetate, propionate, butyrate proportions, and acetate to propionate ratio did not differ (P>0.05) among breeds but differed (P<0.05) between grazing systems. Acetate (P<0.05) and acetate to propionate ratio (P<0.05) were higher in the communal grazing system, while the reverse was true for propionate (P<0.05) and butyrate (P<0.05). Bonsmara produced more methane than Nguni under similar conditions, with Nguni uniquely producing more methane per BW, indicating host genetics influence. Communal animals and older animals produced more CH4 than commercial and younger cows regardless of the breed, indicating ruminal inefficiencies in very old cows. These results emphasize the idea that host genetics or breed, grazing system, and age influence methane output and performance. Hence, breeding strategies for hard-to-measure traits like methane production need to put all these factors into consideration.Thesis (MSc) (Animal Science) -- University of Fort Hare, 202