Study on reproductive performance of Holstein x Lai Sind crossbred dairy heifers and cows at smallholdings in Ho Chi Minh City,Vietnam

The reproductive performance of Holstein x Lai Sind crossbred dairy heifers and cows was evaluated at smallholdings in Ho Chi Minh City (HCMC). The data of 232 heifers and 244 cows (261 lactations) from 35 small dairy farms was collected over a 2-year period, from 2013 to 2014. The overall mean for age at first service (AFS), days between first and last service (DFLS), and age at conception (AC) of heifers was 479 (±80), 38 (±80), and 517 (±114) days, respectively. Average number of services per conception (NSC), conception rate (CR), and conception rate at first service (CRFS) was 1.8 (±1.4), 55, and 58%, respectively. The overall mean for the waiting period (WP), DFLS, and days open (DO) of cows was 109 (±52), 133 (±114), and 242 (±129) days, respectively. The mean for NSC, CR, and CRFS was 4.3 (±2.7), 23, and 14%, respectively. A very significant decrease in AFS and AC according to the year of birth, and a significant increase in AFS according to body weight at first insemination (>320 kg) were observed. The CRFS of heifers inseminated in 2013 was significantly higher than in 2014. Monthly mean CR in heifers and cows was negatively correlated with THI. The WP, DFLS, DO, and NSC of cows significantly decreased according to the year of calving. Cows that calved in rainy season had a significantly longer WP than in dry season. The occurrence of postpartum (PP) diseases was accompanied by an increase in WP, DO, and NSC. A decrease in body condition score (BCS) between calving and 60th day (C60) and also between 60th and 120th day of lactation resulted in a significant increase in WP and DO. A decrease in BCS between C60 was also accompanied by a considerable reduction in CRFS of cows. Season and BCS at insemination had a significant effect on NSC and CR of cows. Reproductive performance was satisfactory for heifers, but poor for cows. Losses of BCS during the first months of lactation and at insemination were the major risk factors for this poor performance. Moreover, the season had a more negative effect on fertility in cows than in heifers.     

The effect of non-genetic factors on the reproductive performance of Sanga and Friesian × Sanga crossbred dairy cattle breeds kept under hot and humid environment

A study was conducted to assess the effect of non-genetic factors on the reproductive performance of Sanga and Friesian?×?Sanga crossbred dairy cattle kept at Amrahia Dairy Farm, Ghana. Records on 66 crossbred Friesian?×?Sanga and 105 purebred Sanga cattle from 2005 to 2012 were used. The effect of sex of calf (male or female), season of calving (major, minor and dry), year of calving (2005–2012) and parity (first to third) on birthweight, calving interval and age at first calving were determined. The data were analyzed using the general linear model procedures of GenStat (Discovery Edition). The effect of parity of dam, year of calving, season of calving and sex of calf were considered as fixed effects for evaluating the different reproductive traits. Data on calving and conception rates over the period were 74.3 and 76.1 %, respectively. The overall mean values for birthweight, age at first calving and calving interval obtained were 23.9?±?1.5 and 22.8?±?1.4 kg, 38.8?±?2.5 and 40.2?±?2.4 months and 390.8?±?12.5 and 413.6?±?12.1 days for the crossbred and Sanga, respectively. It was observed that all the major determinants of reproductive performance studied apart from birthweight were significantly influenced by year of birth, parity, season of calving and sex.     

Reproductive Performance of Crossbred Dairy Cows in Different Production Systems in the Central Highlands of Ethiopia

The study was conducted to examine the fertility status of crossbred dairy cows in mixed crop-livestock production (MCLP), market-oriented specialized dairy production (MSDP) and urban dairy production (UDP) systems, including the Holetta Agricultural Research Center (HARC). Data on general farm management variables and reproductive histories were collected from study farms by questionnaire and from individual cow records. Age at first service and age at first calving were 29.58 months (n = 424) and 40.6 months (n = 348), respectively. Cows managed under UDP were younger at first service and at first calving (p<0.05). The mean intervals from calving to first service and to conception were 141.98 days (n = 284) and 185.02 days (n = 219), respectively. The mean calving interval for cows was 551.82 days (n = 258). Cows in MCLP had longer intervals from calving to first service and to conception and longer calving intervals than those managed under MSDP, UDP and HARC. First service conception rate (43.42%), number of services per conception (1.75) and pregnancy rate (79.29%) did not differ significantly between production systems. Reproductive performance was best in UDP followed by HARC and MSDP. The difference between MCLP and the rest points to particular difficulties in that system. To improve reproductive performance and economic benefit, there should be conservative stocking rate, sensible year-round feeding, a herd health plan, and sustainable extension service.     

Reproductive Disorders of Crossbred Dairy Cows in the Central Highlands of Ethiopia and Their Effect on Reproductive Performance

The study was conducted to estimate the proportion of reproductive disorders and to determine factors affecting reproductive performance of crossbred dairy cows under four different production systems in the central highlands of Ethiopia. The principal postpartum reproductive disorders were retained fetal membranes (14.7%) and uterine infection (15.5%). Anoestrus was the major postpartum reproductive problem in the mixed crop–livestock production system (38.6%) and was significantly associated with this production system. Apart from anoestrus, the occurrence of reproductive disorders was not significantly associated with a production system. Most of the reproductive disorders occurred as a complex rather than as a single abnormality. Two or more abnormal conditions were seen in 11.4% of the cases. Each reproductive trait measured was affected adversely by reproductive disorders. Cows with reproductive disorders in each production system, lactation group and suckling and non-suckling group had longer intervals from calving to first service and to conception (p < 0.001) and required more services per conception (p < 0.001). Pregnancy rate and conception to first service were 84.7% and 51.7%, respectively, for cows without reproductive health problems; and 64.2% and 15.1%, respectively, for cows with reproductive disorders (p < 0.001). Overall, intervals from calving to first service were shorter (p < 0.05) than in younger cows. Intervals from calving to first service and to conception were longer in suckling than in non-suckling cows (p > 0.05). Cows with a good body condition score (>3.5) at calving had shorter calving to first service and conception intervals than cows in poor condition (p < 0.001). The results showed that reproductive abnormalities, coupled with poor body condition, are important factors that contributed to reproductive inefficiency. An appropriate reproductive health management, a reliable artificial insemination service and supplementary feeding could be the management options to reduce or alleviate some of the problems.     

Reproductive performance of Holstein dairy cows in Iran

The objectives of the present study were to describe the current reproductive parameters of Holstein dairy cows in Iran and to determine factors which have a significant effect on reproductive performance with emphasis on high-producing dairy cows. Five large Holstein dairy herds from the major milk production areas of Iran were selected for this study. Reproduction data including parity of dam, calving date, days to first service, days open, number of services, dry period, and occurrence of diseases for cows that calved from 2004 to 2007 were collected from the herds' databases. To determine the effects of year and season of calving, disease status, level of milk production, and parity of dam on reproductive parameters, the proc-mixed procedure in SAS software was used. Overall, data about 8,204 lactation were collected for the study. Results showed that mean (±SD) days open, calving interval, and days to first service for study herds were 134 (±89), 403 (±86), and 67 (±38) days, respectively. Conception rates at the first service and the overall service-conception rate were 41.6% and 41%, respectively. The level of milk production and diseases had significant negative effects on days open and service per conception (P < 0.05); statistical analysis showed that for every 100-kg increase in milk yield, days open will increase by about 0.3 days. However, no significant effect of level of productivity was observed on days to first service. The results of this study indicate that high milk production is a risk factor for decreasing fertility in Iran, like many other parts of the world.     

Reproductive performances of dairy cows in smallholder production system in Selalle, Central Ethiopia

A study was conducted to assess the reproductive performance and factors that influence reproductive efficiency of cows in smallholder dairy farms in Selalle, Central Ethiopia. Three hundred dairy farms (average herd size = 8) were visited and data on reproductive, breeding and management histories were collected and analysed. The overall geometric means for calving to conception interval (n = 382) and duration after last calving (n = 422) were 187 and 201 days in pregnant and non-pregnant cows, respectively. The least-squares mean calving to conception interval was higher (p < 0.05) in mixed crop–livestock production (MCLP) than in small urban dairy production (SUDP) systems and was lower (p < 0.01) in non-suckling than in suckling cows. District significantly influenced (p < 0.01) the least-squares mean duration after last calving and, among the districts, non-pregnant cows in Wuchale-Jida had the highest values, whereas cows in Sululta and Mulo had the lowest values. The overall average number of services per conception (±SD) and the first service conception rate were 1.6 ± 1.0 (n = 382) and 56% (n = 456), respectively. The prevalences of abortion, dystocia (assisted parturition), retained fetal membrane, vulval discharge/endometritis and pre-weaning calf mortality were 1.4%, 1.3%, 5.4%, 2.8% and 17.4%, respectively. The present estimates of extended calving to conception interval and duration after last calving indicate poor reproductive performances of cows in Selalle smallholder dairy farms. The pre-weaning calf mortality rate is highly significant. Accordingly, a further detailed investigation is necessary to identify and quantify the specific reproductive disorders and associated interacting factors attributing to such poor performance and to determine the causes and predisposing factors behind such high calf mortality.     

The association between lameness and fertility in dairy cows

One thousand, four hundred and ninety-one lactations in 770 Friesian, Holstein and Ayrshire crossbred cows have been used to study the associations between lameness and fertility. Lameness was associated with a longer interval between calving and first service and a longer interval between calving and conception. The largest increases in these intervals, of 17 and 30 days, respectively, occurred in cows with either sole or white line lesions occurring between 36 and 70 days after calving. The conception rate during the 63 days before a diagnosis of lameness was made was lower (31 per cent) than at other times (40 per cent).     

Milk production of Jersey and Fleckvieh × Jersey cows in a pasture-based feeding system

Milk production parameters of purebred Jersey (J) cows and Fleckvieh?×?Jersey (F?×?J) cows in a pasture-based feeding system were compared using standard milk recording procedures. Milk, fat and protein production was adjusted to 305 days per lactation and corrected for age at calving. Effects of breed, parity, month and year were estimated for milk, fat and protein yield as well as fat and protein percentage, using the general linear model procedure. Fixed effects identified as affecting milk production parameters significantly were breed, parity and year. F?×?J cows produced significantly more milk than J cows (6141?±?102 and 5398?±?95 kg milk, respectively). Similarly, fat and protein yields were significantly higher in F?×?J (272?±?4 and 201?±?3 kg, respectively) than in Jersey cows (246?±?3 and 194?±?2 kg, respectively). Fat and protein percentages only differed slightly in absolute terms being 4.61?±?0.04 % fat in the Jersey compared to 4.47?±?0.04 % fat in the F?×?J. Protein levels for J and F?×?J cows were 3.62?±?0.03 and 3.51?±?0.03 %, respectively. Despite a lower fat percentage, F?×?J crossbred cows may be more productive than purebred Jersey cows which may be due to heterotic effects.     

Study on reproductive performance of Holstein–Friesian dairy cows at Alage Dairy Farm,Rift Valley of Ethiopia

A retrospective study was carried out to evaluate the reproductive performance of Holstein–Friesian cattle in Alage Dairy Farm in the Rift Valley of Ethiopia using data recorded from July 1983 to June 2005. Data of cows with complete information were considered, and a total of 1,104 records for calving to conception (Cal-Con), calving interval (CI), and number of services per conception (NSC), and 721 records for age at first service (AFS) and at first calving (AFC) were analyzed. The overall means (±S.E.) of AFS, AFC, Cal-Con and CI, and NSC were 991.4 ± 24.3, 1,265 ± 24.3, 285.8 ± 18.9, 561.3 ± 18.9 days and 1.69 ± 0.1, respectively. Parity significantly influenced NSC, Cal-Con, and CI. Season and year showed a significant effect on all the parameters, indicating the role of the environment and more specifically the influence of nutritional conditions at least for the long AFS and AFC, management practices, and climate on reproductive performance of the study herd. A more focused study to discern the elements of the reproductive constraints have been recommended.     

Factors Affecting the First Service Conception Rate of Cows in Smallholder Dairy Farms in Bangladesh

The successful outcome of an insemination is a combination of both male and female fertility‐linked factors. We investigated the first service conception rate of cows at artificial insemination (AI) in the smallholder dairy farms in Bangladesh. Frozen straws were prepared from ejaculates of Bos indicus (n = 7) and Bos indicus × Bos taurus (n = 7) AI bulls. Fertility was determined from 6101 first services in cows that were performed by 18 technicians in four regions between April 2004 and March 2005. Pregnancy was diagnosed by rectal palpation between 60 and 90 days post‐insemination. The Asian version of Artificial Insemination Database Application (AIDA ASIA) was used for bulls‐, cows‐ and AI‐related data recording, and later retrieved for analysis. The mean ± SD number of inseminations performed from individual bulls and their conception rates were 436.0 ± 21.6 and 50.7 ± 1.9%, respectively. Logistic regression demonstrated body condition scores (BCS), heat detection signs, months of AI and their interactions had greatest effects (odds ratios: 1.24–16.65, p < 0.04–0.001) on first service conception rate in cows. Fertility differed (p < 0.02–0.001) between the regions, previous calving months, months of AI, BCS, parity and heat detection signs of cows. Inseminations based on mounting activity (n = 2352), genital discharge (n = 3263) and restlessness and/or other signs (n = 486) yielded a conception rate of 53.6%, 48.8% and 50.1%, respectively (p < 0.05). Conception rate between technicians ranged between 43.4% and 58.6% (p < 0.05). The days interval from calving to first service (overall mean ± SD = 153.4 ± 80.6) had relationship (p < 0.001) with BCS, months of previous calving and parity of the cows. Fertility at AI in smallholder farms can be improved by training farmers on nutrition and reproductive management of the cows.     

Longitudinal observation on reproductive and lactation performances of smallholder crossbred dairy cattle in Fitche,Oromia region,central Ethiopia

A two-year longitudinal study was conducted to assess the reproductive and lactation performances of smallholder crossbred dairy cattle in Fitche, central Ethiopia. Twenty-four smallholder dairy farms were monitored and data on reproductive, breeding, lactation and management aspects of crossbred dairy cows (n = 69) were collected and analysed. Moreover, milk samples were collected and analysed for progesterone. The overall Least-squares means for calving interval (CI), calving to conception interval (CCI) and first observed oestrus after calving were 516, 253 and 141 days, respectively. Suckling significantly prolonged these intervals. The mean first onset of luteal activity (OLA) after calving was 52 days, while 67.4% (n = 43) had a delayed (>55 days) return to cyclicity after calving. Suckling and parity number significantly (p < 0.05) influenced the OLA. The mean lactation length was 54.4 weeks. The overall daily mean milk yield for the first 43 weeks of lactation after calving was 11.7 L/day. The estimated daily milk yield increased slowly and reached peak (13.8 L/day) around the 11th week post partum and declined gradually and steadily. Suckling status, season of calving and parity number significantly influenced the estimated daily milk yield. In conclusion, the present study indicated that the smallholder crossbred dairy cows in the study area had prolonged intervals to first oestrus after calving, to conception and to the next calving, and thus their reproductive performance is unsatisfactory. Delayed first onset of luteal activity (postpartum anoestrus) contributed to these extended intervals. Further detailed investigation is suggested to examine the effects of other relevant factors on the reproductive and lactation performances of smallholder crossbred dairy cows for appropriate intervention.     

Effect of somatic cell count on milk and protein yields and female fertility in Tunisian Holstein dairy cows

The effects of test-day somatic cell scores (SCS) variations on milk and protein yields, and calving to first service and calving to conception intervals were studied in Tunisian Holsteins. There were 34,129, 25,700, and 18,077 test-day production records collected on first, second, and third parity cows, respectively. Records were of cows calving between 1996 and 2004 in 160 herds. Somatic cell scores and milk and protein yields were analysed using a linear model that included herd-test-day date and herd–year interactions, calving season, calving age, and calving to conception interval. Reproductive trait model included herd–year interaction, calving season, calving age, and month of insemination. Effects of SCS on milk and protein yields were studied by regressing current test-day yields on corresponding and preceding test-day SCS, while effects of SCS on fertility traits were investigated by separately regressing calving to first service and calving to conception intervals corrected for environmental and management factors on SCS corrected for actual milk yield. A cow produced around 19.0 kg (SD = 8.0 kg) and 0.6 kg (SD = 0.3 kg) milk and protein yields on a daily basis and had an average of 3.8 (SD = 2.1) SCS in the first three lactations. SCS varied consistently (p < 0.05) with herd-test-day date and herd–year interactions in all lactations. Days in milk, calving age, and calving to conception interval were all together important sources of variation (p < 0.05) for SCS mainly in the first and second parities. Test-day milk and protein yields were unfavourably affected by high SCS recorded in the same test-day and with a lesser degree by SCS observed in the nearest preceding test-day. Reduction in milk and protein productions from increased SCS varied from 0.23 to 1.76 kg and from 6 to 75 g, respectively. Likewise, increased test-day SCS lengthened both calving to first service (mean interval = 94.9 days; SD = 49.1 days) and calving to conception (mean interval = 161 days; SD = 69.6 days) intervals by 1.3 to 2.0 days for each unit increase in SCS. Using SCS in addition to milk traits as a criterion to select semen and improving veterinary care should result in increased milk and protein yields and in satisfactory fertility measures.     

Failure of a single postpartum prostaglandin treatment to improve the reproductive performance of dairy cows

A study was conducted to evaluate the effects of postpartum prostaglandin treatment on reproduction in 3 seasonal calving dairy herds. Recently calved lactating dairy cows were paired on herd, age, calving date and previous production index. One cow in each of the 196 pairs received a single intramuscular injection of 25 mg of the prostaglandin analogue, dinoprost, between 14 and 28 days after calving. Subsequent reproduction was monitored. Within each herd and overall, there was no significant effect of treatment on the intervals from calving to first service, mating start date to first service, calving to conception, mating start date to conception and first service to conception. Treatment also had no significant effect on 21-day submission and pregnancy rates, on the proportion of each group not pregnant at the end of mating, and on first service pregnancy rates. Responses to treatment did not vary between cows calving within 50 days of mating start date and earlier calving cows or between cows aged less than 5 years and older cows.     

Relationships between the plasma concentrations of insulin-like growth factor-I in dairy cows and their fertility and milk yield

The relationships between insulin-like growth factor-I (IGF-I) and the fertility and milk yield of Holstein-Friesian dairy cows were investigated. The concentration of IGF-I in blood was measured weekly from one week before to 12 weeks after calving in 177 multiparous cows and at four times during this period in 142 primiparous cows; the concentration of IGF-I in milk was measured in 50 of the multiparous cows. The plasma concentrations of IGF-I were higher in the primiparous than in the multiparous animals. In the primiparous cows, high concentrations of IGF-I before calving were associated with longer calving to conception intervals. Conversely, in the multiparous cows low concentrations of IGF-I before and after calving were associated with a failure to conceive, despite repeated services. Multiparous cows with IGF-I concentrations of greater than 25 ng/ml in the week after calving were 11 times more likely to conceive to first service than those with lower concentrations. Concentrations of IGF-I greater than 50 ng/ml at first service increased the likelihood of conception five-fold. Cows with higher peak milk yields had lower plasma concentrations of IGF-I and took longer to return to ovarian cyclicity. The negative relationship between milk yield and return to cyclicity was stronger in the multiparous cows (P < 0.002) than in the primiparous cows (P < 0.04). The concentrations of IGF-I in milk followed a different pattern and were not associated with the changes in plasma IGF-I or fertility.     

Fertility Time Trends in Dairy Herds in Northern Portugal

The economics of dairy production are in great part dictated by the reproductive efficiency of the herds. Many studies have reported a widespread decrease in fertility of dairy cows. In a previous work ( Rocha et al. 2001 ), we found a very poor oestrus detection rate (38%), and consequently a delayed calving to 1st AI and calving to conception intervals. However, a good conception rate at 1st AI was noted (51%) resulting in a low number of inseminations per pregnancy (IAP) (1.4). Here, results from a subsequent fertility time trend assessment study carried out in the same region for cows born from 1992 to 2002 are reported. Statistical linear models were used to analyse the data. Estimate linear contrasts of least square means were computed from each model. The number of observations per studied index varied from 12 130 (culling rate) to 57 589 (non‐return rate). Mean age at first calving was 28.9 ± 0.14 months, without (p > 0.05) variation over time. There was a small, but significant (p < 0.05), deterioration of all other parameters. Non‐return rates at 90 days and calving rate at 1st AI decreased 0.3% per trimester, with a consequent increase of 0.04 IA/parturition. Oestrus detection rate decreased 0.13% per year, and calving at 1st AI and calving‐conception intervals increased 0.17 and 0.07 days/year respectively, while intercalving interval increased 1.7 days per year. From 12 130 cows calving, only 1 816 had a 4th lactation (85% culling/losses). The data was not meant to draw conclusions on the causes for the decreased fertility over time, but an increase of milk production from 6537 kg to 8590 kg (305 days) from 1996 to 2002 is probably one factor to take into consideration. Specific measures to revert or slow down this trend of decreasing fertility are warranted. Available strategies are discussed.     

Estimation of genetic parameters for 13 female fertility indices in Holstein dairy cows

This study was aimed to assess genetic parameters for 13 traits in heifers and first-parity Holstein dairy cows. Data consisted of calving and insemination dates of 14,707 Holstein dairy cows in Isfahan province of Iran. Reproductive traits included age at first service (AFS), first service to conception (FSTC), gestation length (GL), age at first calving (AFC), calving to first service (CTFS), days open (DO), calving interval (CI), number of services per conception (NS), and non-return rate at 56 days (NRR). Model equations were optimized using GLM procedure in SAS package following genetic analysis using animal models in ASREML software. Minimum and maximum departure from normal distribution for phenotypic records belonged to AFS, NRR, GL, DO, CI and AFC, NS, FSTC, CTFS, respectively. Estimated heritability varied from 0.002 (NRR) to 0.184 (GL) in heifers and from 0.003 (NRR) to 0.153 (GL) in first-parity cows. AFS, CTFS, and GL were noticeably heritable compared to other assessed traits. Estimated absolute additive genetic correlations were in the range of 0.01 (NRR and AFS) and 0.99 (NRR and NS) in heifers and 0.07 (GL and CI) to 1 (FSTC and CI) in cows. Additive genetic correlations were antagonistic between AFS and other traits, except AFC. Interestingly, NRR which has been included in sire catalogs had the highest average absolute genetic associations with other traits.     

The effects of calving to first service interval on reproductive performance in normal cows and cows with postpartal disease

The relationships between the calving to first service interval and several measures of reproductive performance were evaluated in 1738 lactation records from cows in 32 southern Ontario Holstein herds. Lactation records were divided into three mutually exclusive health categories based on the cows' postpartal disease histories.

Relationships between the calving to first service interval and the first service conception rate, number of services per conception and open interval were similar for all three health categories. The first service conception rate was lower and the average number of services per conception higher in cows first bred before 60 days when compared to cows first bred after 60 days. The relationship between the calving to first service interval and the open interval indicated that for each day that breeding was delayed the open interval was extended by 0.86 days.

It appeared that overall conception rates may be lower for cows first bred very early or very late, but differences in the overall conception rate were only significant for cows experiencing a reproductive tract infection. Unless very expensive semen is being used, it is suggested that disease free cows be bred at the first heat occurring after 40 days postpartum, and that cows experiencing postpartal disease be bred at the first heat occurring after 60 days postpartum.

     

Effect of prostaglandin F2 alpha on the fertility of dairy cows after calving

Three hundred and thirty-one dairy cows in six herds were used to study the effect of a single injection of 25 mg dinoprost, a prostaglandin F2 alpha derivative, administered eight days after calving on several indices of fertility. A detailed comparison was made between 113 treated cows and 113 control cows of the same parity, which had calved within seven days of each other on the same farm and had experienced the same degree of dystocia. In cows which had calved without assistance, the treatment reduced the mean interval between calving and first heat from 40 days to 37 days but increased the mean interval between calving and conception from 83 days to 85 days. In cows which had required assistance at calving, the treatment reduced the mean interval between calving and first heat from 44 days to 34 days and reduced the mean calving to conception interval from 86 days to 68 days. The cows which benefited most were those which had required assistance during their second, third or fourth calvings; their calving to conception intervals were shortened by 22.5 days. An average of 1.39 services was required to establish conception in the treated cows which calved unaided, with 70 per cent conceiving to the first service, compared with an average of 1.34 services per conception and a 72 per cent conception rate to first service for their untreated herdmates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Estimates of genetic parameters for Boran, Friesian and crosses of Friesian and Jersey with the Boran cattle in the tropical highlands of Ethiopia: reproduction traits

A study with the objectives of estimating breed differences, heterosis and recombination effects as well as heritabilities (h²) and repeatabilities (r²) for age at first calving (AFC), calving interval (CI), days open (DO) and number of services per conception (SPC) was conducted using reproduction records collected from 1496 cows comprising purebred Boran (B), Friesian (F), crosses of Friesian and Jersey (J) with Boran breeds. The crossbred cow groups included four F × B crosses [1/2F:1/2B(F₁), 1/2F:1/2B(F₂), 5/8F:3/8B and 3/4F:1/4B], three J × B crosses [1/2J:1/2B(F₁), 1/2J:1/2B(F₂) and 3/4J:1/4B] and one three‐breed cross (1/4F:1/4J:1/2B). The crossbreeding parameters were estimated using a repeatability animal model for CI, DO and SPC, and a unitrait animal model for AFC. The overall least‐squares means estimated were: 38.3 ± 0.26 months, 435 ± 4 days, 145 ± 10 days and 1.58 ± 0.03 (number) for AFC, CI, DO and SPC, respectively. The breed additive effects of F and J were only significant (p < 0.01) for AFC. Relative to B, both F and J additive contributions for AFC were ?5.4 ± 0.5 and ?5.5 ± 1.9 months, respectively. Crossing the B with F and J breeds also resulted in significant heterosis (p < 0.05) ranging from 10 to 21% in all traits. The estimated recombination loss was only significant for AFC (2.8 ± 1.0 months) for F × B crosses. Heritability estimates were high for AFC (0.44 ± 0.05) and low for CI (0.08 ± 0.03), DO (0.04 ± 0.03) and SPC (0.08 ± 0.02). The corresponding estimates for the repeatability (r²) were 0.14 ± 0.02 and 0.14 ± 0.02 for CI and DO, respectively. The permanent environmental effect for SPC was zero. These findings show that breed differences between F or J and B, and the individual cow variations are low for reproductive traits studied, except for AFC. Heterotic effects seem to be the major genetic causes for the improved reproductive performances in both the F × B and J × B crossbred cows.     

Influence of restricted suckling and level of feed supplementation on postpartum reproductive performance of zebu and crossbred cattle in the semi-arid tropics.

This study was carried out in central Tanzania on a group of 45 Zebu and 37 crossbred cows which were 4 to 10 years old. At calving time, the animals were allocated to one of the 4 treatment groups. In addition to free access to grazing for all cows in the study, in group H:AR (n = 18), cows were fed a high level of concentrate supplementation (4kg/day) and calves were artificially reared; in group H:RS (n = 24), cows were fed a high level of concentrate supplementation (4kg/day) and calves were only allowed restricted suckling up until the weaning age of 6 months. In group L:AR (n = 23) cows were fed a low level of concentrate supplementation (2kg/day) and calves were artificially reared; and in group L:RS (n = 17) cows were fed a low level of concentrate supplementation (2kg/day) and calves were only allowed restricted suckling up until the weaning age of 6 months. Milk progesterone was used as a means of determining the postpartum resumption interval (PRI) and the interval from parturition to conception (PCI). The overall PRI was 47.4 +/- 0.4 days and was significantly affected by breed but not by calving season, with crossbred cows exhibiting a shorter PRI than Zebu cows. The effect of the treatments was significant, with cows in the group H:AR displaying a significantly shorter PRI than those in the other groups, while cows in group L:RS showed a significantly longer PRI than those in the other groups. The overall PCI was 149.5 +/- 3.7 days, and was not significantly affected by breed or calving season. The effect of the treatments was significant, with cows in the group H:AR having a significantly shorter PCI than cows in the other groups, while cows in group L:RS showed a significantly longer PCI than those in the other groups. Crossbred cows had higher live weights at calving (299.4 kg) than Zebu cows (272.6 kg), while all cows gained weight during the first 3 months after calving. The treatments had a significant effect on weight gain, with cows in the group H:AR gaining significantly more weight than those in the other groups. Cows which had high live weights at calving exhibited significantly shorter PRI and PCI than the lighter cows. Animals which had gained more than 5 kg during the first month after calving, or which had gained more than 8 kg during the first 3 months after calving, showed significantly shorter PRI and PCI than cows which had gained less weight. The results show that the calf rearing system and the level of feed supplementation interact with each other and can influence the postpartum anoestrous period in Zebu and Zebu crossbred cattle. Increasing the level of nutrition in restricted suckling cows tended to improve the postpartum anoestrous period, but the positive effects of supplementation could not completely compensate for the negative effects of suckling.