Alternative management systems to increase beef production under extensive conditions

["Thesis (Ph.D. (Animal, Wildlife and Grassland Sciences))--University of the Free State, 2016","Beef cattle","Beef industry -- South Africa","Heifers -- Breeding -- South Africa"]

Grobler, Susanna Maria ; ["Scholtz, M. M.","Greyling, J. P. C.","Neser, F. W. C."]

University of the Free State

Others  :  http://scholar.ufs.ac.za/xmlui/bitstream/11660/5400/1/GroblerSM.pdf

瑞士|英语

来源: University of Iowa

【 摘 要 】

South Africa is still a net importer of beef. Therefore, by increasing off take in the beef sector,South Africa can move towards self-sufficiency. With fertility being regarded as one of themain components influencing total beef herd efficiency, it is essential that the quoted calvingpercentage of 62% in the commercial beef sector of South Africa must be improved. If thelong calving seasons can be shortened and the calving percentage increased, more and heaviercalves with a more uniform age can be weaned. Cows that calve early also have a better chanceof conceiving in the next breeding season and are generally seen as the more fertile animalsDevelopment, production and quality of replacement heifers is a crucial component in theextensive beef production system. In general, beef heifers are managed to calve for the firsttime at three years of age, but in some cases mating of heifers at one year of age have beenadvocated.All extensive beef production systems in South Africa are dependent on natural veld and it iswell documented that veld condition have a huge influence on a number of beef productionparameters. Studies conducted on natural veld have concentrated mainly on aspects that affectherd efficiency, including calving percentage, pre-weaning growth and supplementation ofcows and calves. However, none of the studies focused on the reproduction performance ofbeef cattle mated naturally after synchronization, heifer age at breeding and effect of grazingsystem on veld condition.The aim of the study was to evaluate: the effect of estrous synchronization followed by naturalmating on the calving percentage and calving distribution of multiparous beef cows and heifers;effect of breeding heifers at either 14 months or 26 months of age and the evaluation of a highutilized grazing system and controlled selective grazing on veld condition and animalperformance. The effects of climate on cow-calf production characteristics over time was alsoevaluated.The study was conducted from 2009 to 2015 at the Roodeplaat experimental farm (REF) of theARC-Animal Production Institute (25°34'11.27''S; 28°22'05.36''E) on 900 ha of naturalrangeland described as Sourish Mixed Bushveld. The experimental herd (n=92) was dividedin four sub-herds consisting of 23 cows each at the beginning of the project in 2009. It was ensured that the four sub-herds were as uniform as possible at the beginning of the project e.g.age, weight, previous number of calves.Within each sub-herd, 50% of the cows and heifers were synchronized prior to thecommencement of the breeding season. Two sub-herds were subjected to high utilized grazingand two sub-herds were subjected to controlled selective grazing. The two grazing systemswere related to the use of 30% or 60% of the available grass dry matter. Half the heifers weremated at 14 months and the other half at 26 months.Results from this study indicated that calving percentage and body condition score did notdiffer significantly (P=0.54) between cows that was either synchronized or not synchronizedfollowed by natural mating. However, estrous synchronization prior to natural mating didinfluence the average days to conception with synchronized cows calving earlier, except for2012 in the calving season. Over the six-year project period 15% more cows from thesynchronized group conceived within 293 days after the onset of the breeding season. Calvesfrom the synchronized cows weaned on average 5kg heavier than the cows that were notsynchronized although this difference was not significant.Conception rates of heifers mated at 26 months were significantly (P<0.05) higher than heifersmated at 14 months of age. It would seem that it may be more viable to breed Bonsmara heifersin an extensive production system in the Sourish Mixed Bushveld region at 26 months of agefor the first time. Synchronization of 14 month old heifers did not improve conception rateover 14 month old heifers bred naturally. However, the calving percentage of synchronizedheifers bred at 26 months was 6% higher than the non-synchronized heifers.Almost no veld condition change was recorded except for veld condition scores for bothcontrolled selective grazing and high utilization grazing. In addition, the results indicate atendency that high utilization grazing improved veld condition score and grass speciescomposition over that of controlled selective grazing, but the duration of the study is too shortto make a definite conclusion on the effect of grazing strategy on veld condition.It was also shown that grazing strategy did not have a significant influence on cow weight andcalf growth over the six-year period, indicating that both grazing strategies are sustainable inthe Sourish Mixed Bushveld if carrying capacity is adhered to.With the significant differences between years (P �?0.05) for calving percentage, cow weightat calving, cow weight at weaning, calf birth weight, calf weaning weight and body conditionscore over the six-year observation period, the effect of seasonal temperature, relative humidityand rainfall is elucidated. Forward stepwise regression procedures were performed todetermine what climatic data were involved in cow and calf weight at birth and weaning aswell as calving percentage. In spite of the high standard errors (which were probably due tothe small sample size), maximum relative humidity one month prior to the start of the breedingseason, made a major contribution to explain calving percentage and minimum temperaturewithin the last month of the 3 month breeding season, had a low negative correlation withcalving percentage. It can be speculated that high humidity in the study region (Sourish MixedBushveld) is an indication of warm and wet conditions, negatively impacting cow and bullcomfort, leading to lower conception rates. The negative correlation between minimumtemperature within the last month of the breeding season and calving percentage may indicatethat the cows were unable to cool down at night during the warmer summer months of the year,leading to lower conception rates and resorptions.The researcher acknowledge that the available herd size may be a limitation and that a biggerherd or sub-herds' size combined with bigger land size could benefit the project outcome,possibly resulting in more significant differences and/or enhanced interpretation of results.