The objective of this study was to estimate prevalence of (sub) clinical hypocalcaemia, peri- and early post-partum problems and to identify factors associated with (sub) clinical hypocalcaemia, and peri- and early post-natal problems in dairy cows in North-Western Ethiopia. The prevalence of clinical hypocalcemia estimated from the questionnaire data in the current study (5.6%) was much lower than the prevalence reported in previous studies: 30 %, by[12] in Gondar, 27% by [13] in Addis Ababa and 17.5% by [14] in Hawassa dairy herds. This type of variation was supported by the result observed in the 135 controlled trials from the meta-analysis data set used by [17], for which the mean incidence was 21% with a range of 0–83%. It was however, slightly lower than 8% reported by [18] from Zimbabwe. The prevalence of this study was moderately higher than the result reported in American 3. 5% and Australian 3.45% and somewhat lesser than the result 6.17% reported in European studies [9]. The typical prevalence of milk fever varies between 3.5% and 7.0% as reported by Mulligan and Doherty [19]. The lower prevalence in Western world possibly attributed with enhancements in nutritional management practices and better adaptations of these breeds with the climatic condition. However, it is difficult to reunite these variations given that Ethiopian herds produce less milk than Western herds. The frequency of metabolic disorders maybe influenced by climatic conditions [18]. The variation in the extent of UV radiation, regular evaporation rate and the variation between maximum and minimum ambient temperature may meaningfully disturb the occurrence of milk fever [20, 21].
The prevalence of peri- and early post-partum problems in dairy cows recorded in this study revealed that 232(80.6%) of the herds and 459 (30.1%) of the cows involved in the study were affected at least by one peri- or early postpartum problem. Because, to our experience, there is no previous study reported with similar period specific (only on peri-partum and within the first 21 day after caving) problems in Ethiopia, it was not possible to compare our results. From other countries, for instance, from Brazil, Peters et al [22] reported the prevalence of 45.6% and from Florida, Ribeiro et al [23] reported the prevalence of 37.5% clinical problems are higher than from the current result. This variation can be attributed with the spectrum of the problems included in the study, for instance, in our study only reproductive related problems were incorporated but Ribeiro et al [23] incorporated 2.5 % respiratory, 4.0% digestive and 3.2% lameness.
Prevalence of retention of fetal membrane estimated in this study (9.7%) was almost equivalent with prevalence reported in previous studies in Ethiopia (8.6%) reported by Molalegn and Shiv [24], 7.18% by Haile et al. [25] and 8.3% by Ayana and Gudeta [26], However, in other studies, retention of fetal membrane was reported with higher prevalence: 12.91% by Gizaw et al. [27], 14.28% by Mamo [28], (17%) by Haile et al. [25], 18.3% by Degefa et al. [29] and 19.2% by Gashaw et al. [30]. The variation in the prevalence of retention of fetal membrane between different studies may be attributed to the difference in predisposing factors to which the animals are subjected. Among factors, immune-suppression, vitamin and mineral deficiencies, and disease conditions (uterine paresis, abortion, stress, late or premature birth, dystocia, infections, and seasonal and hormonal disorders) have been identified as causes of retention of fetal membrane [31, 32].
The prevalence of clinical metritis estimated in the current study (4.3%) was in agreement with the prevalence of clinical metritis reported by Dhaher et al.[33] who reported clinical metritis with prevalence of (4.0%) and Hadush et al. [34] who reported clinical metritis with prevalence of 3.5%. But, it was slightly lower than prevalence of clinical metritis reported by Ayana and Gudeta, [26] who reported prevalence of 5.6%. These slight differences in prevalence of clinical metritis among studies may be related to differences in study methodology such as sampling and data collection, experience of farmers to clinical metritis. Prevalence of clinical metritis estimated in the current study and other previous studies are much lower than prevalence of clinical metritis reported from some other countries. For instance, from Brazil, Peters et al [22] reported prevalence of 17.3% from a study conducted on grazing dairy cows, Kim and Suh, (2003) reported 17.6% from large confinement herds and Santos et al. [35] reported 16.1%. However, a prevalence clinical metritis which almost equivalent to current study (5.3%) was reported in a study conducted in Florida, USA by Ribeiro et al., [23]. These variations in prevalence of clinical metritis may be attributed to differences in diagnosis, breeds of cows, and difference in the frequency of observation of the cows and other transition management activities [36].
The prevalence of clinical mastitis that occurred during the first 21 days (3 week) after parturition was 8.4%. This result was in agreement with Abuom et al. [37] having the prevalence of 9.7% in Keneya. It was slightly lower than the result reported in Brazile by Peters et al [22] in which an overall prevalence of 11.7% with herd level variations 19.1% 13.2% 10.2% 14.3% and 13.3% in different farms reported.
It is not surprising that if prevalence of dystocia estimated in the current study (4.1%) is in agreement with the prevalence of dystocia (3.4%) reported by Benti and Zewdie [38] and 3.8% by Gashaw et al., [30]. Because the methodology used by Benti and Zewdie [38] was similar with our study. Moreover, both studies were conducted in small holder Holstein Friesian and Zebu cross breed cows. However, prevalence lower or higher than prevalence in the current study was reported. Hadush et al. [34] reported prevalence of 2.9%. Higher prevalence was also reported: 5.7% by Mamo, [28], 7.75 % by Dawit and Ahmed [39] and 5.9% by Haile et al. [25]. This variation in the occurrence of dystocia may be due to the fact that it is influenced by the factors such as parity of the dam, type of nutrition as well as breed of the sire. Inseminating cows with semen collected from large sized bulls without taking into account the size and age of cows is an important factor in precipitating dystocia [25]. In North-Western Ethiopia, dairy farmers are using Holstein Friesian semen to cross with indigenous Zebu cows for better milk yield. The indigenous Zebu cows are smaller in size compared to that of Holstein Friesian. So it is not surprising dystocia to be frequent in North-Western Ethiopian dairy farms. When dairy farmers are planning to cross breed their indigenous Zebu cows with Holstein Friesian semen, they should give priority to select cows and heifers which are larger in body size.
Prevalence of vaginal and uterine prolapse estimated in the current study was consistent with prevalence of vaginal and uterine prolapse reported by Dawite and Ahmed [39], Hadush et al. [34] and Benti and Zewdie [38]. But it was lower than prevalence of vaginal and uterine prolapse reported by Haile et al. [25]. However, prevalence of vaginal and uterine prolapse lower than in the current study were also reported: 0.65% by Bitew and Prasad [24], 0.5% by Gashaw et al. [30] and Woldegebriel [40] who reported 0.4%. This variation might be due to management system (feeding), sample size and breed of animals.
Prevalence of subclinical hypocalcemia was 26.1%. To my knowledge, there is no previous study reported on subclinical hypocalcemia in Ethiopia. However from other countries both lower and higher prevalence compared to the current study was reported. For instance, from Brazil, Peters et al [22] reported prevalence of 20% for subclinical hypocalcemia although a higher prevalence (40%) of subclinical hypocalcemia was reported by Ribeiro et al., [23] from the same country. Subclinical hypocalcemia was also reported at higher prevalence from other countries: 47.6% by Venjakob et al. [41] from German. Jawor et al. [42] reported an increased occurrence of subclinical hypocalcemia with parity: 41%, 49%, 51%, 54%, and 42% in 2nd–6th lactation cows, respectively. The variation in prevalence of subclinical hypocalcemia may be attributed to the breed of cows related to milk yield, and the difference in the feeding management. Types of nutrition and milk yield of cows are risk to subclinical hypocalcemia [43]. In the current study, prevalence of subclinical hypocalcemia was not calculated for different parity cows.
The odds of peri- and post-partum problems specifically milk fever, retention of fetal membrane and clinical mastitis were higher in higher parity cows which was in agreement to other works conducted on general reproductive problems of dairy cows [25, 28, 44]. As literature supports this can be attributed to milk yield increment with parity and can be a risk of calcium deficiency because of the higher milk yield. Besides, parity increases with age and increment in age results decline of immunity of the cows. This leads pluriparus cows to be more prone to Peri-partum problems [41, 45]. In addition, the genital tract of pluriparus cows repeatedly exposed to environmental factors and this can impart uterine infection [25].
The odds of peri- and early post-partum problems: milk fever, retention of fetal membrane, clinical mastitis and clinical metritis were significantly higher (p<0.05) in cows producing higher milk. Similar to our findings, Santos et al. [35] and Ribeiro et al. [23] had observed a high prevalence of clinical diseases in high-producing cows in confine farms. This attributed to loss of large amount of ionized calcium through milk which impairs muscular contraction and results milk fever and associated problems [5, 46, 47]. Moreover, higher amount of milk results in negative energy balance, and cause immune suppression [8, 48].
Prevalence of (Sub) clinical hypocalcemia was significantly higher (p<0.05) on cows produce higher milk yield. Similarly to the current finding, DeGaris & Lean [9] and Caixeta et al. [47] had observed a high prevalence of hypocalcemia in high producing cows. This is attributed in two ways, one is loss of higher volume of calcium through milk and the second is high yielding cows also had a higher energy demand to support milk production and were more likely to acquire a severe energy deficiency after calving than cows with lower yields. This enforces the fat metabolism and develops ketosis that makes the cow anorexic and reduces dietary calcium intake [46].
The odd of (sub) clinical hypocalcemia was significantly higher (p<0.05) in cows with higher parity (at 5 and 6 parity). This association was in agreement with the report stated by DeGaris & Lean [9], Jawor et al. [42] and Reinhardt et al. [10]. The age and parity-associated susceptibility might be related to Ca homeostatic mechanisms. As reviewed by Seifi and Kia [45] with increasing age, the hemostasis process is impeded and results in moderate to severe hypocalcemia. It has been assumed that the number of vitamin D receptors in intestines decline with increasing age. In addition, as animals age increase, the number of receptors for PTH on target tissues decline.
The occurrence of (sub) clinical hypocalcemia was significantly higher (p<0.05) on cows with higher body condition. Similarly to this DeGaris & Lean [9] reported a higher prevalence of hypocalcemia in cows with higher body condition. This is due to over conditioned dairy cows take small amount of calcium this is caused by reduced appetite and with higher BCS at calving have a higher calcium output in milk, making them more prone to hypocalcemia [49].