title: Optimizing age of bull at first use in relation to fertility of Murrah breeding bulls.
abstract: OBJECTIVE
  The aim of the present investigation was to optimize the age at first use (AAFU) of semen of Murrah breeding bulls, which will help in early selection of bulls under progeny testing program for improving the reproductive performance in the herd.
  
  
  METHODS
  The data on AAFU, conception rate based on first A.I. (CRFAI), overall conception rate (OCR), and birth weight (B.WT) of 57 Murrah bulls during 1993-2014 at NDRI center pertaining to 14 sets of Network Project on Buffalo Improvement at ICAR-National Dairy Research Institute, Karnal, Haryana, India were adjusted for significant environmental influences and subsequently analyzed. Simple and multiple regression models were used for prediction of CRFAI and OCR of Murrah breeding bulls. Comparative evaluation of three developed models (I-III) showed that Model III, having AAFU and B.WT, fulfill the accuracy of model as revealed by high coefficient of determination, low mean sum of squares due to error, low conceptual predictive value, and low Bayesian information criterion.
  
  
  RESULTS
  The results revealed that the average predicted CRFAI was highest (39.95%) at <3.5 years and lowest (34.87%) at >4.5 years of age at first A.I/use. Similarly, average predicted OCR was highest (41.05%) at <3.5 years and lowest (39.42%) at >4.5 years of age at first A.I/use of Murrah bulls.
  
  
  CONCLUSIONS
  In organized herd under progeny testing program, Murrah bulls should be used at young age, i.e. prior to 3.5 years, which is expected to result in 5.08% better CRFAI and 1.63% better OCR in comparison to Murrah bulls used after 4.5 years of age.
authors.affiliation: Dairy Cattle Breeding Division, National Dairy Research Institute, Karnal, Haryana, India.
authors.forename: M A
authors.initials: MA
authors.lastname: Mir
authors.affiliation: Dairy Cattle Breeding Division, National Dairy Research Institute, Karnal, Haryana, India.
authors.forename: A K
authors.initials: AK
authors.lastname: Chakravarty
authors.affiliation: Dairy Cattle Breeding Division, National Dairy Research Institute, Karnal, Haryana, India.
authors.forename: A K
authors.initials: AK
authors.lastname: Gupta
authors.affiliation: Division of Animal Genetics, Indian Veterinary Research Institute, Barielly, Uttar Pradesh, India.
authors.forename: B C
authors.initials: BC
authors.lastname: Naha
authors.affiliation: Dairy Cattle Breeding Division, National Dairy Research Institute, Karnal, Haryana, India.
authors.forename: V
authors.initials: V
authors.lastname: Jamuna
authors.affiliation: Department of Animal Genetics and Breeding, Lala Lajpat Rai University of Veterinary and Animal Sciences, Hisar, Haryana, India.
authors.forename: C S
authors.initials: CS
authors.lastname: Patil
authors.affiliation: Dairy Cattle Breeding Division, National Dairy Research Institute, Karnal, Haryana, India.
authors.forename: A P
authors.initials: AP
authors.lastname: Singh
keywords: Murrah bull; age at first use; conception rate based on first A.I; overall conception rate