Implications of negative energy balance in lactating Barki and Rahmani ewes

Abstract

Context During lactation, ewes usually undergo a state of negative energy balance since the energy required for milk production and maintenance of body tissue functions exceeds energy ingested. Aims This study was performed to explore the impact of negative energy balance associated with lactation on milk yield and composition, metabolic profile and some reproductive traits in two different breeds of sheep. Methods In total, one hundred lactating Barki and Rahmani ewes (50 ewes per breed) were used for six consecutive parities to investigate the effects of breed, parity, week of lactation, and their interactions on milk yield and composition, including percentages of milk fat and milk protein, fat–protein ratio, energy-corrected milk, milk energy value, energy balance, some serum metabolites and reproductive traits. Milk and blood samples were collected weekly throughout the study. Key results Rahmani ewes had higher milk fat %, fat yield, protein %, protein yield and milk energy value, but lower fat–protein ratio than did Barki ewes. The greater value of energy balance and accumulated negative energy balance from parturition to energy balance equilibrium and fewer days from lambing to energy balance equilibrium were observed in Rahmani than in Barki ewes. Greater values of serum concentrations of total protein, albumin, cholesterol and lower values of aspartate aminotransferase and alanine aminotransferase were recorded in Rahmani than in Barki ewes. Reproductive traits, including days to the first oestrus and days to conception, recorded greater values in Barki than in Rahmani ewes. Conclusion Rahmani ewes possessed adaptive characteristics to the challenge of lactation, expressed as a lower value of fat–protein ratio, which indicated a tendency of energy balance stabilisation, than did Barki ewes. This tendency was reflected in improved reproductive traits by reducing days to first oestrus and days to conception in Rahmani compared with Barki ewes. Implications Lactation presents a critical stressful period in the dam productive life because of the high nutritional and other managerial requirements necessary for milk production. This study was conducted to assess and compare the sustainability of the two sheep breeds to the production expenditure during lactation.