Fertility in a tropical beef herd divergently selected for pregnancy rate

Hetzel, David J.; Mackinnon, M. J.; Dixon, R. M.; Entwistle, KW

doi:10.1017/s0003356100004268

Cited by 28 publications

(17 citation statements)

References 3 publications

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“…This behaviour predisposes young calves to wild dog attack -the age that also coincides with the time when most calves disappear and are recorded as 'unknown losses' in reproductive performance studies (e.g. Rankine and Donaldson 1968;Entwistle 1974;Holroyd 1977;Hetzel et al 1989;Burns et al 2010). In contrast, when cows and calves return to their herd, the behaviour of adult cattle to cooperatively protect calves, by mobbing against wild dogs if they threaten calves and forming crèches of up to 20 calves in the custody of two or three adult cattle, helps to deter wild dog attacks.…”

Section: Discussionmentioning

confidence: 99%

“…Most of the losses of calves were found to occur within 14 days of birth and the largest proportion of loss was from unknown causes, where the calf carcass could not be found (Holroyd 1987a). In reviewing calf losses across northern Australia, Holroyd (1977) found that post-natal loss ranged from 2.3 to 31.4% and mostly occurred within 1 month of birth (see also Hetzel et al 1989; where 75% of calf losses were found to occur between the last trimester of pregnancy and 2 months of age), where the extensive nature of northern Australia's beef cattle industry and the lack of any intensive investigations were believed the cause why most calf losses were classed as 'unknown'. In reviewing calf losses between confirmed pregnancy and weaning over the last 25 years, Burns et al (2010) concluded that the large range of causes of peri-natal mortality rates remains poorly understood, with little progress made in determining causes of peri-and post-natal calf mortalities.…”

Section: Introductionmentioning

confidence: 99%

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Wild dog control impacts on calf wastage in extensive beef cattle enterprises

Allen¹

2014

Anim. Prod. Sci.

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Abstract. Wild dogs (Canis lupus dingo and hybrids) are routinely controlled to protect beef cattle from predation yet beef producers are sometimes ambivalent as to whether wild dogs are a significant problem or not. This paper reports the loss of calves between birth and weaning in pregnancy-tested herds located on two beef cattle properties in south-central and far north Queensland for up to 4 consecutive years. Comparisons of lactation failures (identified when dams that previously tested pregnant were found non-lactating at weaning) were made between adjoining test herds grazed in places with or without annual (or twice annual) wild dog poison baiting programs. No correlation between wild dog relative abundance and lactation failures was apparent. Calf loss was frequently higher (three in 7 site-years, 11-32%) in baited areas than in non-baited areas (9% in 1 of 7 site-years). Predation loss of calves (in either area) only occurred in seasons of below-average rainfall, but was not related to herd nutrition. These data suggest that controlling wild dogs to protect calves on extensive beef cattle enterprises is unnecessary in most years because wild dogs do not routinely prey on calves. In those seasons when wild dog predation might occur, baiting can be counter-productive. Baiting appears to produce perturbations that change the way surviving or re-colonising wild dog populations select and handle prey and/or how they interact with livestock.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Wild dog control impacts on calf wastage in extensive beef cattle enterprises

Allen¹

2014

Anim. Prod. Sci.

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“…Although applying high selection intensities to lowly heritable traits can circumvent this problem, for example with beef cow reproduction (Hetzel et al 1989) or with litter size in sheep (Clarke 1972), another method of improving pregnancy rate in beef cattle could be to select on more highly heritable, correlated traits. An experiment of this type was set up by one of us (GLB) at Ruakura beginning with the mating/ calving years of 1981/1982.…”

Section: Introductionmentioning

confidence: 99%

Genetic parameters for growth, puberty, and beef cow reproductive traits in a puberty selection experiment

Morris

Wilson

Bennett

et al. 2000

New Zealand Journal of Agricultural Research

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A selection experiment to change reproductive traits in Angus cattle has been maintained for 14 years, with first calvings in 1985. Alongside an unselected control line, three lines were established, selected for increased age at puberty in heifers (AGE+ line), reduced age at puberty in heifers (AGE-line), or increased scrotal circumference (SC line). The last two lines were merged at the 1992 matings, with the revised objective of applying further selection in both sexes to reduce age at puberty in heifers. Dates at puberty in heifers from an average of 8 to 16 months of age and SC in bulls were recorded in all lines, along with the pregnancy rates (PR) and subsequent calving dates (CD) in heifers and all cow-age groups. Heritabilities of single-record SC, standardised age at first behavioural oestrus (SFO), and single-record CD were 0.41 ± 0.04 (repeatability 0.70 ± 0.01), 0.27 ± 0.04, and 0.09 ± 0.04 (repeatability 0.19 ±0.03), respectively. Genetic correlations of SC with SFO and CD were -0.25 ± 0.09 and -0.23 ± 0.15, respectively; SFO with CD 0.57 ± 0.17; and PR with SFO and SC-0.36 ±0.13 and 0.12 ± 0.11, respectively. The selection-line difference in PR over seven years (AGE-mean minus AGE+ mean), excluding yearling heifer matings, was 4.7 ± 2.1% (P < 0.05). Mean CD in the AGE-line was 3 days earlier than in the AGE+ line (P < 0.09). These correlation and selection-line results suggest that selecting for higher SC and earlier heifer puberty leads to earlier CD and higher PR.

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“…This is consistent with a herd of 445 Droughtmaster cows, where those that lactated in the previous season had a 10% higher calf survival rate than those that did not lactate in the previous season (Hetzel et al, 1989). Given the low repeatability of foetal and calf mortality as reported in above studies, physical abnormalities, e.g.…”

Section: General Risk Factors Influencing Calf Survivalsupporting

confidence: 87%

Dehydration as a risk factor for calf mortality in northern Australia

Muller¹

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It is estimated that approximately one million calves die in Australia every year, with the majority unexplained. This thesis reviews losses associated with dehydration-mediated mortality during neonatal life, when there is highest risk of mortality, and reports three studies of neonatal calf dehydration.For 12 neonatal Brahman calves at Spyglass research site (northern forest land type, Queensland), variation in hydration status was investigated (Experiment 1). Change in live-weight from birth was used as the primary measure of hydration. Half of this cohort had low live weight gain between birth and day 3 of life (p = 0.01) compared to calves growing at 0.95±0.24 kg/day from birth. Low growth and associated reduced plasma protein (p = 0.04) in 6 calves indicated reduced colostrum, milk uptake and therefore reduced body fluid replenishment compared to other calves. This positions them at high risk of mortality under adverse environmental conditions. Urea space was tested as a measure of body water; however, percentage body water estimates were unrealistically elevated (> 80% of live weight) and therefore not representative of actual calf percentage body water.Descriptive analysis of risk factors for calf mortality was conducted for 478 and 378 tropically adapted newborn calves, respectively at Spyglass and Brian Pastures (southern forest land type, central Queensland) research sites (Experiment 2). The incidence risk of neonatal mortality in the southern forest of Queensland and northern forest of Queensland was 3.1% and 4.7%, respectively. Some risk factors and the percentage of calves exposed to high mortality risk included: dam body condition score ≤2 (8%), birth weight ≤28 kg (18%), low birth vigour (2%), large udder size (1%), at least two large teats (2%) and poor maternal protectiveness (5%). The low proportion of cows in poor body condition and good nutritional management limited the opportunity for dehydration-mediated neonatal mortality. There were no cases of prolonged heat stress around calving at the level previously associated with foetal and calf mortality. Experiment 2 indicates that low calf mortality may be achieved in any country type, provided that a low proportion of calves are exposed to high risk of mortality. A simple mechanistic model was developed to describe milk uptake volumes and ambient temperature (heat stress) impacts on neonatal hydration. This model provided clarification for the possible risk of dehydration mediated mortality across breeding herds of northern Australia.This thesis demonstrated variation in milk delivery, modelled that low milk delivery is associated with dehydration-mediated mortality and demonstrated that risk of mortality is low at a herd level when the risk factors associated with reduced milk delivery have low frequency.3

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Fertility in a tropical beef herd divergently selected for pregnancy rate

Cited by 28 publications

References 3 publications

Wild dog control impacts on calf wastage in extensive beef cattle enterprises

Wild dog control impacts on calf wastage in extensive beef cattle enterprises

Genetic parameters for growth, puberty, and beef cow reproductive traits in a puberty selection experiment

Dehydration as a risk factor for calf mortality in northern Australia

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