Hickson Re

Dystocia in beef heifers: A review of genetic and nutritional influences

Abstract Breeding beef heifers for the first time at 15 months of age has potential to increase the efficiency of the beef breeding-cow herd. An increased incidence of dystocia in heifers calving at 2 years of age, compared to mature cows, is a major reason many farmers in New Zealand have not adopted the practice. The predominant type of dystocia affecting 2-year-old heifers is feto-maternal disproportion, a condition in which the fetus is too large relative to the size of the heifers pelvis. Reducing birthweight of the calf is a means of reducing the incidence of dystocia. Birthweight and length of gestation are determined by genotype of the calf, maternal genetic effects and environmental effects. Bulls with low estimated breeding values for birthweight have been selected for mating heifers; however, the positive genetic correlation between birthweight and mature weight meant that the progeny of these bulls tended to be lighter at finishing, making them less desirable in the beef industry. The genotype of the dam also plays a role in determining the risk of dystocia; the maternal ability of the dam to nurture the fetus influences birth- weight, and the dams genetic potential for growth influences the size of her pelvic area. Heavy heifers tend to produce high- birthweight calves, counteracting the reduction in the incidence of dystocia resulting from the larger pelvis in larger heifers. Manipulating feeding level during pregnancy offers an alternative method for manipulating the birthweight of calves. Little is known about the effects of nutrition in early gestation on placental development or birthweight of calves. No differences in the birthweight of calves have been observed in response to variation in feeding in mid-pregnancy, and variable responses in birthweight and the incidence of dystocia to feeding in the third trimester of pregnancy have been reported. Differences in birthweight have not always resulted in differences in the incidence of dystocia, primarily due to differences in liveweight of the heifer also induced by feeding regimens. Variability in the incidence of dystocia in response to feeding level in the third trimester of pregnancy makes it difficult to make recommendations for the feeding of heifers at this stage of gestation. More research is needed into the effects of nutrition in early gestation on fetal and placental development in cattle.

Effect of twin-bearing ewe body condition score and late pregnancy nutrition on lamb performance

This study aimed to investigate the effects of ewe body condition score and nutrition on twin-bearing ewes and their offspring. At maximum Day 112 of pregnancy (range 96–112 days), 185 twin-bearing ewes were allocated to either a ‘Medium’ or ‘ad libitum’ (Adlib) feeding treatment for the following 25 days (P112–P136). Each feeding treatment included ewes of body condition score: 2.0 (CS2.0, Medium n = 32, Adlib n = 28), CS2.5 (Medium n = 31, Adlib n = 33) or CS3.0 (Medium n = 30, Adlib n = 31). After P136 ewes were offered Adlib feeding conditions. Medium treatment ewes were lighter (P 0.05) on lamb liveweight or apparent colostrum intake. Ewe body condition score had no effect (P > 0.05) on lamb birthweight or apparent colostrum intake. Lambs born to CS2.0 ewes had greater (P 0.05) no effect of condition score on total litter liveweight. In conclusion, these results suggest twin-bearing ewes of body condition 2.0–3.0 can be offered restricted feeding levels to at least Day 136 of pregnancy with few implications for their lambs.

Genetic parameters for production traits in New Zealand dual-purpose sheep, with an emphasis on dagginess

Genetic and phenotypic parameters were estimated for production and disease traits (including dagginess) from about 2 million pedigree-recorded animals born between 1990 and 2008 in New Zealand dual-purpose ram breeding flocks. This is the most comprehensive study of genetic parameter estimates for the New Zealand sheep industry to date and includes estimates that have not previously been reported. Estimates of heritability were moderate for BW at 8 mo (LW8), fleece weight at 12 mo (FW12), dagginess score at 3 and 8 mo (DAG3, DAG8; 0.31 to 0.37), typical for weaning weight (WWT), fecal egg count in summer (FEC1) and autumn (FEC2), and analogous Nematodirus counts (NEM1, NEM2; 0.17 to 0.21), and low for number of lambs born to ewes (NLB; 0.09). The genetic correlations among production traits, WWT, LW8, and FW12, were positive and moderate to high. Correlations of DAG3 and DAG8 with production and disease traits were low and mostly negative. The NLB had low, but typically positive, correlations with other traits. Disease traits also had low, but positive, correlations with production traits (WWT, LW8, and FW12), and were highly correlated among themselves. In general, the heritability estimate for BW and dagginess were greater than what is currently used in the New Zealand genetic evaluation service (Sheep Improvement Limited), and the availability of accurate estimates for dagginess plus parasite resistance and their genetic correlations with production traits will enable more accurate breeding values to be estimated for New Zealand sheep.

Effects of body condition score and nutrition in lactation on twin-bearing ewe and lamb performance to weaning

This study investigated the effect of feeding and body condition during late pregnancy and lactation on both ewe and lamb performance until weaning. On day 141 of pregnancy, ewes with a body condition score (BCS) of 2.0, 2.5 or 3.0 were allocated a ‘Low’, ‘Intermediate’ or ‘High’ feeding treatment until weaning at day 79 of lactation. Feeding treatments had no effect on lamb live weight at birth, summit metabolic rate or indices of colostrum intake (P > 0.05). At weaning, lambs born to the High treatment were heavier than the Intermediate treatment, which were heavier than the Low treatment (P < 0.05). Lambs reared by ewes with a BCS of 2.0 were lighter during the lactation period than lambs whose dam had a BCS of 2.5 or 3.0 (P < 0.05). In addition, lambs reared by ewes with a BCS of 2.0 had greater summit metabolic rates and greater survival to weaning than those reared by BCS 3.0 (P < 0.05) but not BCS 2.5 (P > 0.05). There was, however, no effect of feeding treatment on lamb survival to weaning. These results indicate that, within these BCS, benefits could be gained from greater BCS in late pregnancy across all feeding treatments.

Genetic relationships between dagginess, breech bareness, and wool traits in New Zealand dual-purpose sheep

Genetic and phenotypic parameters were estimated for dagginess, breech, wool, and fiber traits from approximately 29,500 progeny born in 2009 and 2010 in New Zealand dual-purpose ram breeding sheep flocks. Dagginess is adherence of fecal matter to the wool, and this study investigates the genetic and phenotypic correlations between dagginess and breech and wool traits. Estimates for heritability were moderate (0.21 to 0.44) for the following traits: dag score at 3 and 8 mo (DAG3, DAG8), breech bareness, wool length, wool bulk (BULK), mean fiber diameter, mean fiber diameter SD, mean fiber diameter CV, curvature (CURV), weaning weight at 3 mo, and autumn BW. Heritability estimates for fleece weight at 12 mo and proportion of medullated fibers were high (0.49 and 0.53, respectively). Dag score at 3 mo and DAG8 had low genetic and phenotypic correlations with all traits. Breech bareness had positive genetic and phenotypic correlations with CURV and BULK and mostly negative genetic correlations with all other wool traits. In summary the quantity and attributes of wool were not primary causative factors in fecal accumulation, leaving fecal consistency and composition as the major factors.

Genetic parameters for milk components including lactose from test day records in the New Zealand dairy herd

There are currently few published estimates of genetic parameters for lactose yield or lactose percentage for dairy cows. Recent trends in milk standardisation for whole milk powder have resulted in whole milk being standardised with the ratio of protein to protein-plus-lactose of at least 0.39. Currently whole milk powder produced from New Zealand milk has a protein to protein-plus-lactose ratio of 0.43, thus requiring additional lactose to be imported to maximise the return from the current product portfolio. Estimates of genetic parameters were obtained using 15,366 test day records from 4378 first-lactation cows in the Livestock Improvement Corporation sire proving scheme in the 2011–12 dairy season, distributed across 70 herds. These data included milk, fat, protein and lactose yields; fat, protein and lactose percentages; somatic cell count; days in milk; and the protein to fat ratio and protein to protein-plus-lactose ratio. Mean milk yield was 13.8 L/day, containing 5.16% fat, 3.93% protein and 5.12% lactose. Heritability estimates were 0.22, 0.35, 0.32 and 0.25 for milk yield, fat, protein and lactose percentages, respectively, which were lower than those reported in the literature but enough to allow for selection of lactose percentage.

Effects of liveweight gain during pregnancy of 15‐month‐old Angus heifers on dystocia and birth weight, body dimensions, estimated milk intake and weaning weight of the calves

Abstract First‐calving, 2‐year‐old heifers are particularly susceptible to dystocia caused by foeto‐maternal disproportion. Forty‐four 15‐month‐old Angus heifers were allocated to either a moderate (583 ± 73 g/day) or low (193 ± 71 g/day) liveweight gain treatment for the first trimester (93 days) of pregnancy. Both groups were of similar liveweight at parturition. Birth weight of the calves and incidence of dystocia were not significantly different between treatment groups at 33.0 ± 0.7 kg, compared with 33.8 ± 0.6 kg and 12% compared with 22% for the moderate and low groups, respectively. Body dimensions, liveweight from birth to 205 days of age and estimated milk intake of the calves were generally not affected by treatment. Assisted calves had greater estimated milk intake than unassisted calves at 37 days of age (5.9 ±1.0 versus 4.1 ± 0.6 kg/day; P < 0.05). Liveweight gain in early pregnancy did not affect birth weight of calves or the incidence of dystocia in 2‐year‐old heifers.

Nutritional restriction of triplet-bearing ewes and body condition score has minimal impacts

Abstract At day 115 of pregnancy, 155 triplet-bearing Romney ewes were allocated to either a ‘Medium’ or ‘ad-libitum’ (Adlib) feeding treatment until P136. Both feeding treatments included ewes with body condition scores of 2.0, 2.5 and 3.0. Medium treatment ewes were lighter and had lower body condition scores (P<0.05) than Adlib ewes at the end of the feeding period. Ewe feeding treatment had no effect (P>0.05) on lamb birth weight or colostrum intake. However, lambs born to Adlib ewes had lower (P<0.05) survival but were heavier (P>0.05) at weaning, resulting in no effect of feeding treatment on total weight of lamb weaned per ewe. Ewes with a body condition score of 2.0 reared less (P<0.05) total weight of lamb to weaning than 2.5 ewes, suggesting management plans should ensure that ewes with low condition scores are avoided. These feeding results indicate that triplet-bearing ewes can be managed with post-grazing masses of ≈900 kg DM/ha until day 136 of pregnancy with minimal impacts.

Profitability of calving heifers at 2 compared with 3 years of age and the effect of incidence of assistance at parturition on profitability

There is potential to increase the profitability of beef-breeding cows in New Zealand by calving heifers for the first time at 2 instead of 3 years of age; however, calving at this earlier age is often associated with an increase in assistance at calving. This study used a simulated farm system within the Grazing Systems Model to estimate the profitability of calving heifers at 2 years of age with various incidences of assistance at calving. Annual profit from the beef cattle herd was greater for primiparous 2-year-old heifers than for 3-year-old primiparous heifers when the incidence of assisted calving in 2-year-old heifers was less than 89%. Replacement rate increased with increased assistance at parturition. These results indicated that a considerable gain in profitability could be made by calving heifers for the first time at 2 instead of 3 years of age, and further gains could be made in herds already calving heifers at 2 years of age by reducing the incidence of assistance at calving.

Duration of parturition and frequency of abdominal contractions in primiparous, 2-year-old Angus heifers and the relevance of body dimensions of calves to dystocia

The predominant cause of dystocia in 2-year-old heifers is feto–maternal disproportion, and consequently, birthweight of the calf explains much variation in dystocia. This experiment was carried out to identify other factors in addition to birthweight that contribute to the probability of dystocia. Seventy-three primiparous, 2-year-old Angus heifers were observed continuously during the calving period and record was made of the time at which various events occurred during parturition. Frequency of abdominal contractions was lower 30 min after onset of parturition than at 60–180 min after onset of parturition (P < 0.05). The longest stage of parturition was the time from the first abdominal contraction until the appearance of amnion, while the time from the appearance of the head until delivery of the calf was the shortest stage. Frequency of abdominal contractions was negatively correlated with duration of parturition. Duration of parturition was less than 135 min for 75% of the non-assisted heifers. Body dimensions of calves did not explain any additional variation in dystocia beyond that explained by birthweight and sex of calf and postpartum liveweight of the heifer. Calves that had an assisted birth took longer to attempt to stand, to stand and to suckle after birth than non-assisted calves. Within the non-assisted calves, there was no impact of duration of parturition on these behaviours of the newborn calf. In conclusion, body dimensions of the calf did not contribute to the probability of dystocia, but more frequent abdominal contractions contributed to a shorter duration of parturition. Behaviour of newborn calves was adversely affected by dystocia.