Non-genetic factors affecting dystocia and its effects on milk production of Holstein dairy cows in Morocco

I Boujenane

Department of Animal Production and Biotechnology, Institut Agronomique et Vétérinaire Hassan II, Rabat, Morocco
ismail.boujenane@gmail.com

Abstract

The objective of this study was to analyze the effects of non-genetic factors affecting calving difficulty and to investigate the effect of dystocia on 305-day milk and fat yields and fat percent of Holstein cows in North of Morocco. The data set consisted of 1770 calving records for the period from July 2008 to December 2012. Calvings were visually scored on a 5-point system of difficulty with increments of 1. Factors influencing dystocia were analyzed using gamma regression in the GENMOD procedure.

The average incidence of dystocia was 4.24%. Dystocia was significantly influenced by calving year and birth number/sex combination (P<0.001), but not significantly affected neither by parity nor calving season (P>0.05). Parturitions that occurred in 2008 were associated with more calving difficulty than those occurring during other calving years, with a decreasing trend of dystocia from one year to the other. The least-squares means of dystocia scores decreased from 1.92 in 2008 to 1.32 in 2012. Calving difficulty was significantly influenced by birth number/sex of offspring (P<0.001). Cows giving birth to single males had a probability of dystocia higher than dams of single females. The least-squares means for scores of dystocia were 1.40 and 1.33, respectively. Moreover, dystocia was significantly influenced by birth number. Thus, the probability of dystocia was higher in cows giving birth to twins than in those with singles. However, the Chi-Square tests indicated that the differences among dams giving birth to twin females, twin males and twin female and male were not significantly different (P>0.05). The 305-day milk yield, fat yield and fat percent were not significantly affected by dystocia (P>0.05) although cows with dystocia produced 182.8 kg, 7.4 kg and 0% less than cows without dystocia, respectively.

Keywords: calving difficulty, dairy cattle, nutrition

Introduction

Dystocia, more commonly known as difficult calving, is becoming a greater concern for cattle breeders because it is a major cause of calf mortality at or shortly after birth, decreased rebreeding efficiency and great economic losses (Berger 1994; Dekkers 1994; Mee 2004; Mee 2008). Internationally, reported prevalence of dystocia in dairy cattle varied from 2 to 22% (Mee 2008). The most common cause of dystocia is a physical incompatibility between the pelvic size of the dam and the size of the calf, i.e. when a small cow trying to give birth to a large calf. Thus, dystocia is affected by factors attributed to the dam as well as to the calf (Bellows et al 1969). Furthermore, dystocia is associated with a reduction in milk yield in the subsequent lactation (Meijering 1984; Dematawewa and Berger 1997; Berry et al 2007; McGuirk et al 2007; Barrier and Haskell 2011; Haskell and Barrier 2014). In Morocco, the farmers believe that the calves are the only income from dairy industry because the marketable milk is barely used to finance the maintenance expenditure of cows. Therefore, the farmers try to get calves that are heavy at birth because they have a high likelihood to reach a heavy weight at marketing. This practice is very often accompanied with calving difficulty in cows. Nevertheless, the prevalence and the risk factors of dystocia in dairy herds of Morocco have never been studied.

The objective of this research was to identify non-genetic factors associated with calving difficulty and to assess the effect of dystocia on milk production. Such information could be beneficial in determining procedures to develop management techniques to minimize calving problems in the breeding herd.

Material and methods

Herd management and studied variables

Data were collected in a private dairy herd in northern Morocco. This herd was used because of the completeness of its records. All cows in the herd were Holstein. Average age at calving was 47.6±15.8 months, ranging from 23 to 82 months, and average lactation number was 2.31±1.06, ranging from 1 to 4. During the study, mean milk production per cow was 8066±1956 kg per 305 days of lactation.

All cows were housed in free-stall barns. They were observed for estrus two times daily, at 0900 h and 1500 h. Cows detected in estrus were inseminated within 1 h after detection of estrus. Pregnancy was confirmed by rectal palpation 55–65 days after artificial insemination. All lactating cows were fed the same diet that was formulated to meet the nutrient requirements for a lactating Holstein cow weighing 650 kg and producing 25–35 kg of milk/day.

The farm milked cows in fully automated milking parlors (Boumatic, USA) equipped with automatic milking machine. Cows were milked two to three times daily according to their lactation stage. Teat dipping was routinely performed at milking.

Information was recorded between July 2008 and December 2012. It included cow identification, birth date, calving date, parity, birth number (single vs. twin), calf gender, 305-day milk and fat yields, fat percent and calving score. For this last information, calvings were visually assessed by the farmer and a dystocia score was subjectively assigned according to the degree of assistance provided. Dystocia scores ranged from 1 to 5 (1= no assistance= natural, 2= slight assistance, 3= considerable assistance, 4= considerable force needed, and 5= complicated= veterinary assistance required).

Statistical analyses

The initial data file included 1937 records. After editing, cows with missing or doubtful data and with productive records out of range were deleted from the analyses. Discarded records represented 8.62% of the initial data. Finally, 1770 records were analyzed. To assess the effects of factors associated with dystocia, the gamma regression in GENMOD procedure (SAS 2002) was applied. The statistical model included fixed effects of parity (3 levels: 1, 2 and 3 or greater), calving season (3 levels: January – April, May – August and September – December), calving year (5 levels: 2008, 2009, …, 2012) and birth number/sex of offspring combination (5 levels: single/female, single/male, twins/females, twins/female and male and twins/males). Moreover, contrasts were computed to test the effect of sex alone and the effect of birth number alone.

The effects of dystocia on subsequent cow 305-day milk and fat yields and on fat percent were determined using the Proc GLM (SAS 2002). Fixed effects included in the model were parity (3 levels: 1, 2 and 3 or greater), season of calving (3 levels: January – April, May – August and September – December), year of calving (5 levels: 2008, 2009, …, 2012) and dystocia (2 levels: easy calving (dystocia scores of 1 or 2) and difficult calving (dystocia scores of 3 or greater)). For all these analyses, the two-way interactions were tested, but they were not found significant (P>0.05).

Results and discussion

Incidence of dystocia and effects of risk factors

The distribution of cows calving scores is presented in Figure 1. Of 1770 calvings, 4.2% were considered as difficult (dystocia score ≥ 3), whereas 95.8% were considered as easy calvings. The incidence of dystocia recorded in the present study was in line with the findings of Gürcan et al (2014) (4.3%), but lower than the previously documented dystocia incidence (Berry et al 2007; Fiedlerova et al 2008; Mee et al 2008; Atashi et al 2012a) although twin births were included in this analysis, which most of researchers did not.

Figure 1. The distribution of calving scores of Holstein cows

Parameter estimates, confidence intervals and least-squares means from gamma regression for dystocia are presented in Table 1. Parity of cows was not a significant source of variation for dystocia (P>0.05). This finding is not in agreement with those of Atashi et al (2012a) who reported that first-parity cows were more likely to have a difficult calving relative to older cows because heifers have never before given birth and they usually are not full grown.

Likewise, calving season did not significantly influence dystocia (P>0.05). This result is in conformity with those of Olson et al (2009) and Johanson et al (2011) who reported that there was no significant effect of calving season on dystocia, although the latter team found that incidence of dystocia was slightly higher in winter than in summer. However, this result is not consistent with that of Atashi et al (2012b) who reported that the season of calving significantly affected calving difficulty, where the lowest dystocia frequency was observed when parturition occurred in summer and fall, and with that of Gürcan et al (2014) who found that the incidence of dystocia was lower for cows in winter, autumn and spring than in summer. They indicated that this might be related with heat stress since high temperatures in summer may influence the process of parturition which might result with dystocia. Inversely, Johanson and Berger (2003) reported that dystocia is more frequent in cows calving in winter than those calving in summer because their calves need more assistance since they are heavier than calves born in summer.

Calving year had a significant effect on dystocia (P<0.001). Parturitions that occurred in 2008 were associated with more calving difficulty than those occurring during other calving years, with a decreasing trend of dystocia from one year to the other. The least-squares means of dystocia scores decreased from 1.92 in 2008 to 1.32 in 2012. This dropout corresponds to the use few years before of service sires with low dystocia evaluations, especially for matings to first calf heifers. Moreover, the result of Chi-Square tests indicated that the difference between years 2008 and 2009 was not significant (P>0.05), whereas those among the other calving years were significant (P<0.01 to 0.001). This result is in agreement with that of Gürcan et al (2014) who reported different incidences of dystocia at different calving years.

Calving difficulty was significantly influenced by birth number/sex of offspring (P<0.001). Cows giving birth to single males had a probability of dystocia of 19.6% higher than dams of single females. The least-squares means for scores of dystocia were 1.40 and 1.33, respectively. This result agrees with the previously documented association between sex of calf and dystocia (Johanson and Berger 2003; Berry et al 2007; Atashi et al 2012a). The high dystocia incidence in cows that delivered a male calf might be explained by the fact that male calves, being larger and heavier at birth, cause more problems than females. However, this is not the only cause, since Berry et al (2007) and Atashi et al (2012b) showed that the effect of sex on dystocia remained despite the inclusion of calf birth weight in the statistical model in singletons, indicating that differences between calf sex other than birth weight influence dystocia.

Moreover, estimating the contrasts, dystocia was significantly influenced by birth number. Thus, the probability of dystocia was higher in cows giving birth to twins than in those with singles. The difference in scores of dystocia between dams of twins and singles was about 0.46. Additionally, the Chi-2 tests indicated that the differences among dams giving birth to twin females, twin males and twin female and male were not significant (P>0.05). The high risk of dystocia in cows giving birth to twins compared to those with singles is in agreement with the findings of Atashi et al (2012b) who reported that the risk of dystocia was considerably higher when twin births occurred, but differences were not found in cows which gave birth to two calves.

Dystocia effects on milk production

The effects of dystocia on milk production are summarised in Table 2. The 305-day milk yield, fat yield and fat percent were not significantly affected by dystocia (P>0.05) although cows with dystocia produced 182.8 kg, 7.4 kg and 0% less than cows without dystocia, respectively. This is consistent with the findings of Tenhagen et al (2007) who reported that mild and severe cases of dystocia had no significant effects on milk production, but milk production in cows after caesarean section was reduced by 5 to 10% on the first 6 milk test-days postpartum, with no significant difference observed in late lactation. However, the result of the current study is not in agreement with that of Atashi et al (2012a) who reported reductions in 305-d lactation performance of 56.6 kg of milk and 1.87 kg of fat in first lactation, whereas corresponding values were 722.6 kg of milk and 17.52 kg of fat for fourth lactation. Moreover, it seems that dystocia influenced early lactation milk yield but its effects disappear beyond the first phase of lactation. Thus, Lombard et al (2003) showed that cumulative milk production to 30 days in milk significantly decreased as dystocia score increased (P<0.05), whereas cumulative 90-day milk production and mature equivalent milk were not significantly decreased as dystocia score increased. Berry et al (2007) reported on grazing dairy cows in New Zealand that total 60- and 270-d milk yields were 42.0 and 61.9 kg less, respectively, in cows that experienced dystocia at calving compared with those that did not. Furthermore, in Finnish Ayrshire cows, Rajala and Grohn (1998) reported no significant effect of dystocia on early lactation milk yield in first-parity cows, although postpartum was found in second-parity cows that experienced dystocia. Also, Dematawewa and Berger (1997) reported that losses are thought to be greater with increasing degrees of difficulty. Djemali et al (1987) reported that decreases in 305-day ME milk in Holstein cows with dystocia score 5 (extreme difficulty) versus score 1 (no problem) were 465, 576, and 725 kg in the first, second, and third and greater lactations, respectively. Atashi et al (2012a) concluded that different definitions of dystocia and different statistical methods used to estimate milk loss due to dystocia could be of the main sources of these discrepancies.

Conclusion

• Under the conditions of this study, the incidence of dystocia was low. Moreover, dystocia had no significant effects on reduced milk production during lactation of Holstein cows.
  
  
• Because cows producing female calves have lower incidence of dystocia than those producing male calves, using sexed semen to produce female calves or service sires with low dystocia evaluations, especially for matings to first calf heifers, may be an interesting management practice for reducing dystocia.

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Received 5 April 2017; Accepted 9 May 2017; Published 1 August 2017

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