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Milk Yield, Nitrogen Use Efficiency, and Rumen Fermentation in Barki Ewes, and the Performance of Their Offspring in
Ibrahim M Khattab1, Adel M Abdel-Wahed2, Ahmed A Aboamer3
1Department of Animal and Fish Production, Faculty of Desert and Environmental Agriculture, Matrouh University, Matrouh, Egypt.
Abstract:
This study investigated the effects of increasing dietary crude protein (CP) levels on milk yield, nutrient utilization, nitrogen use efficiency, rumen fermentation, and lamb growth in lactating Barki ewes. Twenty-one multiparous ewes (mean body weight (BW) of 40.5 ± 0.41 kg), each nursing one lamb (mean BW: 6.22 ± 0.16 kg), were randomly assigned to three total mixed rations containing 13.0%, 15.1%, and 17.1% CP on a dry matter (DM) basis, respectively, in a randomized complete block design over a 70-day lactation period. Results indicated a linear increase (p < 0.05) in milk yield, alongside higher milk fat, protein, and lactose yields, as dietary CP levels rose. Crude protein intake increased linearly (p = 0.001) as dietary CP levels elevated. Apparent digestibility of organic matter, CP, neutral detergent fiber (NDF), and acid detergent fiber (ADF) also increased linearly (p < 0.05). Diets with 15.1% and 17.1% CP demonstrated higher (p < 0.05) CP, NDF, and ADF digestibility compared to the 13.0% CP diet. Nitrogen (N) intake, milk N, urinary N, urea-N, fecal N, and plasma urea concentrations increased linearly (p < 0.05) with increasing dietary CP levels. Ewes receiving 17.1% CP excreted higher (p < 0.05) amounts of urinary N, urea-N, and fecal N. Ruminal ammonia-N concentrations increased linearly (p = 0.001) with dietary CP levels, peaking (p = 0.001) in ewes on the 17.1% CP diet, followed by those on 15.1% and 13.0% CP diets. Molar proportions of isobutyrate and isovalerate increased linearly (p < 0.05) with higher dietary CP. Microbial protein content increased linearly (p = 0.001), attaining higher values with 15.1% and 17.1% CP diets (p = 0.010) compared to 13.0% CP. Lambs final BW and average daily gain (ADG) improved linearly (p = 0.001) as dietary CP levels increased, with 15.1% and 17.1% CP diets yielding superior outcomes over 13.0% CP diet. In conclusion, increasing dietary CP from 13.0% to 17.1% linearly improved digestibility, milk yield, and lamb growth. The 15.1% and 17.1% CP diets enhanced ruminal fermentation, but 17.1% CP maximized nitrogen excretion. Thus, 15.1% CP is recommended to optimize productivity and nutrient utilization in semi-intensive Barki ewe production systems.
