Effects of Milk Urea Nitrogen (MUN) and Climatological Factors on Reproduction Efficiency of Holstein Friesian and Jersey Cows in the Subtropics.

Edward Cottington Webb,Elandri De Bruyn

doi:10.3390/ani11113068

Edward Cottington Webb, Elandri De Bruyn

Open Access

https://doi.org/10.3390/ani11113068

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Abstract

Simple SummaryBlood urea nitrogen (BUN) affects the reproduction of dairy cows, but it is challenging to measure routinely. Milk urea nitrogen (MUN) is a useful proxy for BUN, but the effects of MUN and climatological factors on the reproduction efficiency of dairy cows in the subtropics, which is characterized by extreme temperature and humidity indices, are lacking. The present study investigated the effects of MUN and climatological factors on the reproduction efficiency of Holstein Friesian and Jersey cows in South Africa. The results confirm that MUN influences the reproduction efficiency of dairy cows in the subtropics. High MUN, relative humidity, and maximum daily temperatures compromise the reproduction of Holstein Friesian cows. Jersey cows have a lower threshold MUN concentration compared to Holstein Friesian cows, but they are not adversely affected by high humidity or temperatures.This study investigated the effects of MUN and climatological factors on the inter calving period (ICP), reproductive performance (RP%), and reproductive index (RI) in Holstein Friesian (n = 1177) and Jersey cows (n = 3305) in different seasons in the subtropics. Threshold values for MUN on the reproduction of dairy cows in the subtropics remain controversial due to complex environmental interactions, especially with high environmental temperatures. A retrospective analysis was conducted of data obtained from the National Milk Recording scheme of the Agricultural Research Council (ARC) in South Africa. The results confirm that MUN influences the reproduction of dairy cows in the subtropics. MUN concentrations exceeding 18.1 ± 4.28 mg/dL in Holstein Friesian cows and 13.0 ± 4.70 mg/dL in Jersey cows extended the inter calving period (ICP), and decreased RP% and RI. Jersey cows have a lower threshold MUN concentration compared to Holstein Friesian cows, but they are not adversely affected by high humidity or temperatures, while Holstein Friesian cows are.

Highlights

Conception and reconception rates of high-producing dairy cows remain problematic in modern dairy production systems [1], especially in the subtropics
The composition of the total mixed rations (TMR) fed to Holstein Friesian and Jersey cows was comparable to that generally fed to dairy cows in this subtropical region of South Africa and that used in other studies [32,33]
The effect of milk urea nitrogen (MUN) on the reproduction efficiency of dairy cows is significant in Holstein Friesian and Jersey cows in the subtropics, but their susceptibility to excessive MUN concentrations depend on climatological factors such as minimum and maximum daily temperatures and relative humidity

Summary

Introduction

Conception and reconception rates of high-producing dairy cows remain problematic in modern dairy production systems [1], especially in the subtropics. Apart from the major effects of nutrition and specific nutrients on the reproduction of dairy cows, other risk factors such as negative energy balance, inflammation, and impairment of the immune response have been shown to affect reconception rates in a highly cause-and-effect related way [1]. Dietary energy levels interact with blood urea nitrogen (BUN) and may influence the pregnancy rates of dairy cows [2]. High BUN concentrations may indicate inefficient use of dietary nitrogen (N) in the body [2]. Balancing dietary protein and energy ratios may lead to decreased N losses to the environment and increased production efficiency [4]. By holding protein intake constant with increasing levels of energy in the diet, BUN concentrations are likely to be lowered [5]

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