«Department of Ruminant Science, Agriculture University of Szczecin, Poland RENATA PILARCZYK and JERZY WÓJCIK Comparison of body weight and ...»
As expected, the mean body weights of the cows measured in our study proved larger than those reported earlier by other authors. The cows analysed in this study were imported in 1995-1996, thus when the intensive selection had already improved their growth and increased their frame sizes as well as body weights. As a result of the fact the imported cows and their progeny were systematically sired by high-quality Canadian and American bulls, the genetic merit of the animals has been maintained. In our study, the average body weight of the Red Angus cows ranged from 484 kg, on the 1st calving, to 682.9 kg, on the 6th calving, whereas for the Hereford cows it was, respectively 504.3 kg and 690.1 kg. According to previous reports (NADARAJAH et al., 1984; MARLOWE and MORROW, 1985; SACCO et al., 1990), body weights of 2- to 7-year-old Angus cows ranged from 411 to 510 kg, whilst those of Hereford cows ranged between 402 and 523 kg (FIELD et al., 1988; SACCO et al., 1990). Later studies by GREGORY et al. (1992) revealed increasing average body weight, which in 2- to 7-year-old Hereford cows ranged from 428 to 579 kg and in Angus from 423 to 557 kg. In the study by ARANGO et al. (2004), the mean body weights of 2-, 3-, 4-, 5and 6-year-old Angus cows were already 466, 523, 541, 548, and 542 kg, respectively, and those for Hereford were 476, 545, 576, 579, and 604 kg, respectively.
Comparing the mean body weights of the Red Angus vs. Hereford cows, we have observed that the latter were heavier after all calvings. Differences reaching 40-60 kg were found until the 3rd calving, falling to 7-12 kg after the 5th calving. FRAHM and MARSHALL (1985) reported that Hereford cows are characterised by larger body weights than Angus cows. Also according to GREGORY et al. (1992) Hereford cows were heavier than Angus cows, with the differences ranging from 5 kg (two-year-old cows) to 22 kg (7 years of age). SACCO et al. (1990) have found that Hereford cows between 3 and 4 years of age were heavier than Angus cows by as little as 6 kg.
According to ARANGO et al. (2002), on the other hand, Angus and Hereford cows attained similar weights, except for 6- and 7-year-old Angus cows, which were slightly larger than Hereford cows.
PILARCZYK and WÓJCIK: Comparison of body weight and reproduction performance in cows Differences in the mean body weights of mature cows of the studied breeds are not very high, therefore we can assume that the body sizes of the breeds have rather been equalised, which confirms that the selection for larger frame sizes of Red Angus and Hereford cattle carried out for decades has been successful.
Selective breeding in beef cattle has been focusing on increasing the growth rates.
However, whatever the production system, reproductive traits appear to be the most economically important in a beef cattle improvement program. In fact, reproductive traits dramatically affect productivity. Nevertheless, no suitable selection criterion exists due to the difficulty of finding easily measurable traits under paddock mating (the most frequent case in beef cattle) which are genetically related to reproduction.
Calving interval is the chosen trait to measure cows’ fertility. (GOYACHE and GUTIERREZ, 2001) Calving interval after the first calving found in the present study was unsatisfactory.
The parameter improved considerably after the 2nd calving in the Simmental, Salers, and Limousin cows, and after the 3rd calving in the Herefords. The Red Angus cows exhibited too long calving intervals after all calvings, which should be considered as unfavourable. Extension of subsequent calving intervals may have resulted from displaced calving dates; beef cows that calve late in the given year often maintain this date in the following year or do not conceive at all (PATTERSON et al., 1992).
PRZYSUCHA et al. (2002) found the longest calving intervals being after the 1st calving as well as the 4th calving and those to follow. WERTH et al. (1996) reported that young beef cows have longer periods of postpartum anestrus than mature cows and frequently have calving intervals that are longer than 365 days. Cows at 2 years of age tend to have a longer postpartum interval to time of conception (SHORT et al., 1990). Two-year-old cows are still growing during gestation, and the fetus is also competing for nutrients. If the cow is stressed nutritionally, nutrient needs of the fetus are met first, and any of the dam’s energy stores are subject to depletion. After calving, young cows must satisfy their own growth, maintenance, and lactation requirements, as well as replenish their own depleted energy stores before initiation of estrous cycles will occur (SHORT et al., 1990; WERTH et al., 1996). The calving intervals observed in our study were similar to those reported by other authors in other Polish herds of beef cattle (LITWIŃCZUK et al., 2001; POGORZELSKA et al., 1999).
The common opinion that the analysed breeds differ considerably in calving ease and mature body weight was not confirmed in this study, which implies that great changes have undergone in the success of the selection. In the early 1970s, as demonstrated by LASTER et al. (1973), calves sired by Charolais, Simmental and Limousin bulls experienced significantly more calving difficulty than those sired by Hereford and Angus bulls. No significant differences in percent calving difficulty were found among the Charolais, Simmental, Limousin. Hereford cows had more calving difficulty than Angus cows. Recent studies by ERIKSSON et al. (2004) have revealed that the Charolais and Hereford breeds, considered as extremes in terms of calving ease, were characterised by a very similar percentage of calving difficulties. The authors report that the total frequency of difficult calvings was 6.6 % for Charolais and 6.2 % for Hereford at first parity and 1.0 % for Charolais and 1.2 % for Hereford at later parities.
The incidence of stillbirth was also higher in heifers (5.9 % for Charolais and 5.6 % for Hereford) compared with older cows (1.8 % for both breeds).
Arch. Tierz. 51 (2008) 4 Studies carried out on Polish herds (PIASECKI et al., 2000; LITWIŃCZUK et al., 2001; STENZEL et al., 2001) show that calving difficulties, depending on the breed and management system, may reach up to 8 % of parturitions (2-4 % most frequently), while the mortality rate may range from 6 % up to 14 % under very extensive conditions, abortions percentage may reach 3.5 %, while the percentage of stillbirths may be 5 %. The highest incidence of calving difficulties was recorded in this study on the first calving. KRZYWDA et al. (2002) report that relatively highest rate of calving difficulties are observed with the first calving; however, such disturbances usually cease naturally or mere human assistance is needed.
Stillbirths and dystocias can result in direct losses due to calf mortality, dam mortality and premature culling, as well as indirect costs due to additional veterinary services, labour and treatment (MCDERMOTT et al., 1992; GOYACHE and GUTIERREZ, 2001). For dystocia, individual calf and dam factors have been reviewed by a number of authors (MEIJERING, 1984; MCDERMOTT et al., 1992). The size of the calf is considered to be the most important determinant (NAAZIE et al., 1989; BENNET and GREGORY, 2001; ERIKSSON et al., 2004).
A large calf in relation to the inlet pelvic dimensions of the cow is the most common cause of dystocia (NAAZIE et al., 1989) and is more important in heifers than in cows (MEIJERING, 1984). KOOTS et al. (1994) reported positive genetic correlations between birth weight and perinatal mortality, suggesting that in most studies, birth weight was larger than optimum. In a review presented high direct genetic correlations between birth weight and calving ease of -0.73 and -0.67 for cows and heifers, respectively. BENNETT and GREGORY (2001) reported direct and maternal genetic correlations of 0.81 and 0.34, respectively, between birth weight and calving difficulty for beef cattle.
Calving difficulty and stillbirth generally have higher incidences in the first parity vs.
later parities (MCDERMOTT et al. 1992; ERIKSSON et al., 2004). ERIKSSON et al.
(2004) state that although the average birth weight of calves from heifers was 7 to 10 % lower than for calves of later parity cows, heifers were also smaller than cows and the frequency of difficult calvings was considerably higher at first parity compared with later parities.
Posterior or abnormal presentations of the calf, weak labour, uterine torsion, and insufficient dilatation of the cervix are of importance especially in older cows (MEIJERING, 1984). According to MCDERMOTT et al. (1992), dystocia in cows was associated with calf sex, previous calving assistance, and large breed type and birth weight; however, in heifers difficult calvings were associated with large breed type and calf birth weight.
The present study has revealed that out of 15 stillborn calves, 7 passed through a difficult labour, whereas more than a half (8 calves) was born from normal parturitions. In several studies (BERGER et al., 1992; MCDERMOTT et al., 1992;
ERIKSSON et al., 2004) more than half of the stillborn calves did not have difficult calvings. The causes of stillbirth for calves with easy or normal calvings are largely unknown (MEIJERING, 1984; DARGATZ et al., 2004).
The incidence of dystocia observed in this study should be considered low, which is a good news. Ranging between 1.2 % and 2.7 %, calving difficulties were to a large extent due to the management system that allows the cows to move freely, but also due PILARCZYK and WÓJCIK: Comparison of body weight and reproduction performance in cows to a low body weight at birth, estimated in the study by PILARCZYK and WÓJCIK (2007) as ranging between 30.0-34.8 kg for heifer calves and 30.7-35.8 kg for bull calves.
According to MCDERMOTT et al. (1992), dystocia rates were lowest for herds calving on pasture and increased through the barn/pasture, barn/yard and closed barn calving location categories. Stillbirths for both cows and heifers were associated with calving assistance, particularly hard assistance. However, a significant proportion of stillborn calves were delivered without assistance.
The breeder should always keep in mind while selecting for weight at birth that excessive body weight of the calf will lead to increased mortality at parturition, whereas lower body weight will be negatively reflected in the growth rate and, consequently, in the profitability of the production (BENNETT and GREGORY, 2001).
Although calf losses due to dystocia can probably be reduced by providing assistance at parturition, there is no clear means of preventing early-term abortions, late-term abortions, or stillbirths (KIRKPATRICK, 2002).
In typical beef herds, twins are a relatively unusual event. Reviews on the genetics of twinning (RUTLEDGE, 1975) suggest that twinning rate in beef breeds is typically less than 5 %. Increasing the incidence of twin births in cattle is one method to increase productivity of beef cattle. However, the opinion KIRKPATRICK (2002), twin birth is undesired by most beef producers for its association with a number of detriments, including lower perinatal calf survival and poorer cow reproductive performance.
Regarding cow performance, twinning is associated with increased dystocia (due to malpresentation), increased incidence of retained placenta, greater frequency of abortion in twin gestation, and longer interval from parturition to first estrus.
To recapitulate, a comparison of the reproductive performance of the cows revealed large variations between the analysed breeds in terms of the calving interval. The best results were achieved by Simmental and Limousin, whereas Red Angus was the worst breed in this respect. An effect of subsequent calving on the calving interval was also demonstrated with the longest calving interval found after the 1st calving and the shortest after the 3rd calving, with a growing trend after subsequent calvings. The breeders are advised to pay particular attention to these critical periods. The most calving difficulty incidents were observed at the 1st calving. During the analysed period, abortions and stillbirths accounted for 1% of pregnancies, except for the Hereford group where 2.8 % stillbirths were recorded. We have also noted a large percentage of twin births in the analysed herds, ranging from 0.5 to 3.5 %, the most among the Simmental cows. This has not, however, caused any decrease in reproductive performance of the cows of this breed. The parameters observed can be considered good, except for the long calving interval in the Red Angus cows. The fact that the cows have been systematically sired by prime-quality polled bulls from the USA or Canada allows presumption that the positive trends in the developing Polish beef cattle production will be maintained.
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