Resources required for calf rearing on New Zealand dairy farms when mating programmes are altered to produce less bobby calves : case study and scenario analyses : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science, Massey University, Palmerston North, New Zealand

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Each year in New Zealand (NZ), approximately 2 million calves are slaughtered before 30-days of age. These ‘bobby calves’ are unsuitable for dairy or beef production due to sex, low-genetic merit, and breed. Growing concern from the public regarding animal welfare is pressuring the NZ dairy industry to reduce bobby calves, to continue to receive a ‘social license’ to farm. One option to reduce bobby calves is for dairy farmers to utilise more sexed and beef-breed semen in mating programmes. However, changing mating programmes to produce more beef calves, also changes resources required for calf rearing and management decisions, such as shed capacity, milk demand, and labour. These changes need to be quantified to help farmers determine the most appropriate mating programmes. The objectives of this project were to; 1) identify and quantify the resources required to house and feed calves born on five case-study herds with different mating programmes and, 2) use these data to predict the resources required on an average NZ dairy farm with different mating programmes aiming to reduce bobby calves. Data collected from the farms included calf outcome, birth and exit weights, and age upon exiting the calf shed. These data were then used to calculate calf growth rates and predicted feed and shed capacity requirements for each case-study herd. These data were also used in an analyses to determine the resource requirements of an average NZ dairy farm (444-cow spring-calving herd) if bobby calves were reduced from the national average of ~35% to a target of ~22% or ~0% of calves within the herd. The aim of the scenario analyses was to identify risks and opportunities of different mating programmes implementing strategies (e.g., using sexed semen and more beef-breed semen) aimed at reducing bobby calves. From the five case-study herds, mating programmes designed to reduce the number of bobbies results in greater calf-rearing resource requirements, particularly calf feed and shed capacity. Outputs from the scenario analyses indicated that a spring-calving herd in NZ produced 40%, 20%, and 7% bobby calves from mating programmes targeting 35%, 22% and 0% bobby calves, respectively. There were greater requirements for milk and shed capacity when bobby calves were reduced to 20% and 7% in Scenarios 2 and 3, respectively, compared to the base Scenario 1 (40% bobby calves). Milk demand increased by 43% when bobby calves decreased from 40% in Scenario 1 to 7% in Scenario 3. Peak shed capacity increased by 11 and 17 calves for Scenarios 2 and 3, respectively, compared with Scenario 1. Peak shed capacity was reached earlier for both Scenarios 2 (day 35) and 3 (day 28), compared with Scenario 1 (day 48). The duration of peak shed capacity increased by 7 days and 12 days, for Scenarios 2 and 3, respectively, when compared to Scenario 1. Before mating programmes are designed to reduce bobby calves, the greater resource requirements and cost of rearing calves must be budgeted for each farm.
Figure 6 (=Yang et al., 2018 Fig 1) was removed for copyright reasons.