Abstract
Aim:The study was to evaluate the relationship between the first service conception (FSC) and milk urea nitrogen (MUN) in smallholder dairy farms under heat and humidity stress.Materials and Methods:Dairy cows from 43 dairy farms giving birth between November 2014 and April 2015 (n=295) contributed to the study. All cows were sampled monthly to measure milk compositions, and we collected additional farm data from farmers through a questionnaire. The first service during the first 120 days of lactation was the outcome of interest in this study. Multivariable logistic regression determined significant associations with FSC.Results:The overall FSC was 22% and the mean MUN concentration was 11.55 mg/dl. The final FSC model included MUN concentration, the season of breeding, and protein energy ratio (PE ratio) in the diet. The odds of FSC were reduced by approximately 10% for each mg/dl higher MUN on the day of the milk sample that was nearest to the artificial insemination (AI) day. The odds of FSC were nearly 3 times higher when the first insemination occurred in winter compared to summer first services. Taking into account the nutritional factors, the odds of FSC were nearly 70% higher with an increase in PE ratio of 10 g of crude protein/Mcal from the mean of 35.90 g.Conclusion:This study of smallholder dairy farmers in the hot and humid climate of Thailand confirmed that season, nutritional management, and MUN concentration were associated with FSC. MUN appears to be a useful indicator to monitor the effects of diet on reproductive performance from this study.
Highlights
The formation of urea in the liver occurs to reduce tissue toxicity of ammonia above amounts utilized by ruminal microbes [1,2]
The odds of First service conception (FSC) were reduced by approximately 10% for each mg/dl higher Milk urea nitrogen (MUN) on the day of the milk sample that was nearest to the artificial insemination (AI) day
This study of smallholder dairy farmers in the hot and humid climate of Thailand confirmed that season, nutritional management, and MUN concentration were associated with FSC
Summary
The formation of urea in the liver occurs to reduce tissue toxicity of ammonia above amounts utilized by ruminal microbes [1,2]. Urea is transported from the liver through blood circulation to other body parts and diffuses into other tissues, for instance, the udder and uterus [3]. Milk urea nitrogen (MUN) can be advantageously used for evaluating urea levels in tissue because the MUN level highly correlates well with blood urea nitrogen level and is obtained through non-invasive techniques [2], often through monthly milk testing programs. First service conception (FSC) has been negatively correlated with MUN in temperate climates [5,6]. In areas with hot and humid summers but moderate winters, such as Florida, the effect of MUN on fertility appears to be modified by weather; cows exposed to high MUN in the summer had lower conception but not in the winter [7]
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