نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه علوم دامی، دانشکده کشاورزی، دانشگاه ایلام، ایلام، ایران
2 موسسه تحقیقات علوم دامی کشور، سازمان تحقیقات آموزش و ترویج کشاورزی، کرج، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
The aim of this study was to investigate the effect of reducing level of rumen undegradable protein (RUP) and rumen-protected lysine and methionine supplementation on dry matter intake (DMI), milk yield and composition and total tract nutrients digestibility of dairy cows in early lactation. Twelve multiparous (parity = 2; average milk yield = 48 ± 1; days in milk = 80 ± 2) Holstein dairy cows were used in replicated 4×4 Latin square design (4 treatments in 4 periods). Each period lasted 21 d with 14 d of experimental diets adaptation and 7 d of data recording and sample collection. The experimental diets included 1- diet containing 17.32% crude protein (CP) without rumen-protected lysine (RPL)and methionine (RPM) supplementation (CP17.32-NoRPL-NoRPM), 2- diet containing 16.08% CP and 0.045% RPM (CP16.08-RPM0.045%), 3- diet containing 15.18% CP and 0.075% RPM (CP15.18-RPM0.075%), and 4- diet containing 14.2% CP, 0.105% RPM, and 0.037% RPL (CP14.2-RPM0.105%-RPL0.037%). Results showed that the lowest DMI was observed in cows fed CP14.2-RPM0.105%-RPL0.037% and CP15.18-RPM0.075% diets compared to others (P<0.05). Milk yield, 4% fat corrected milk, energy corrected milk and milk component production were not affected by the experimental diets (P<0.05). Experimental diets did not affect total tract apparent digestibility of dry matter (DM) and organic matter (OM) (P<0.05). The highest total tract apparent digestibility of CP were observed in cows fed CP17.32-NoRPL-NoRPM (P<0.05). Overall, feeding CP15.18-RPM0.075% diet improved productive performance of Holstein dairy cows in early lactation.
کلیدواژهها [English]
Extended Abstract
Introduction
Protein is one of the major challenges in the livestock industry, especially the dairy cattle industry. Less than 25% of crude protein (CP) consumed is retained in the body of dairy cows and the rest is excreted into the environment in various forms. The reason for this is the high requirement of high-producing dairy cows for protein sources, which are mainly supplied from plant sources. The amino acid (AA) profile of plant protein sources is not in line with the needs of dairy cows, so the efficiency of protein is low. In addition to reducing efficiency, this increases production costs and environmental pollution, and ultimately wastes the country's resources. If protein in the diet is properly balanced, utilization efficiency of dietary protein for milk synthesis reaches 30 to 33% and higher. That is, 30 to 33% of CP consumed is converted into milk protein. However, if the protein balance of the diet is not maintained, this efficiency decreases to 23%. Therefore, reducing nitrogen (N) losses and improving utilization efficiency of N in dairy cows is essential for biological, economic and environmental reasons. One strategy to increase N efficiency is to feed dairy cows diets with low CP content. However, this strategy is usually associated with lower productivity (milk production, milk protein production or both) and is economically undesirable. Therefore, adding essential AAs to low CP diets may be an effective way to maintain milk production and reduce environmental N excretion in dairy cows. Lysine and methionine are two limiting AAs for dairy cows. Adding rumen-protected lysine and methionine to low-protein diets is considered as an efficient method to meet AA requirements. Therefore, the aim of the present study was to investigate the effect of diets containing different levels of CP and rumen-protected methionine and lysine on dry matter intake (DMI), milk yield and composition, and nutrient digestibility in Holstein dairy cows in early lactation.
Materials and Methods
Twelve multiparous (parity = 2; average milk yield = 48 ± 1; days in milk = 80 ± 2) Holstein dairy cows were used in replicated 4×4 Latin square design (4 treatments in 4 periods). Each period lasted 21 d with 14 d of experimental diets adaptation and 7 d of data recording and sample collection. The experimental diets included 1- diet containing 17.32% CP without rumen-protected lysine (RPL)and rumen-protected methionine (RPM) supplementation (CP17.32-NoRPL-NoRPM), 2- diet containing 16.08% CP and 0.045% RPM (CP16.08-RPM0.045%), 3- diet containing 15.18% CP and 0.075% RPM (CP15.18-RPM0.075%), and 4- diet containing 14.2% CP, 0.105% RPM, and 0.037% RPL (CP14.2-RPM0.105%-RPL0.037%). The DMI, milk yield and composition, and nutrient digestibility were measured at last 7-d of each experimental period. Data of this experiment were analyzed using SAS statistical software and PROC MIXED procedure. The mean of the treatments were compared using the Tukey test, and the effects of factors in the model were considered significant at a probability level of less than or equal to 0.05, and a tendency to significance was considered at a probability level of greater than 0.05 and less than or equal to 0.10.
Results
Results showed that the lowest DMI was observed in cows fed CP14.2-RPM0.105%-RPL0.037% and CP15.18-RPM0.075% diets compared to others (P<0.05). Milk yield, 4% fat corrected milk, energy corrected milk and milk component production were not affected by the experimental diets (P<0.05). Milk fat percentage tended to be higher in cows fed CP14.2-RPM0.105%-RPL0.037% and CP15.18-RPM0.075% diets compared to others (P=0.07). Milk protein, lactose and solid not fat were not affected by dietary CP level and RPM and RPL supplement (P<0.05). The highest total solid percentage and the lowest concentration of milk urea nitrogen (MUN) were observed in cows fed CP14.2-RPM0.105%-RPL0.037% and CP15.18-RPM0.075% diets compared to others (P<0.05). Experimental diets did not affect total tract apparent digestibility of dry matter (DM) and organic matter (OM) (P<0.05). The highest total tract apparent digestibility of CP were observed in cows fed CP17.32-NoRPL-NoRPM (P<0.05).
Conclusion
The results of this study showed that the reduction of RUP level without providing essential AAs decreased production performance of dairy cows during early lactation. However, addition of protected lysine and methionine supplements compensated the negative effects of RUP reduction and improved milk yield and composition. These results indicate that diet modification based on the appropriate provision of essential AAs can help improve the production performance, milk quality and nutritional efficiency of dairy cows. This study emphasizes the importance of accurate nutrient supply in dairy cow diets, especially in the early lactation period. Furthermore, these findings can help producers for designing optimal nutritional strategies to improve the efficiency and productivity of their dairy cows.
This article contains all the data that were created or evaluated during the research.
The authors would like to sincerely thank the members of the Faculty of Animal Sciences, University of Tehran Research Council for the approval and support of this research.
The author declares no conflict of interest.
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