Subclinical mastitis in dairy cows in major milk-producing areas of Sri Lanka: Prevalence, associated risk factors, and effects on reproduction.

Compared with clinical mastitis, the subclinical form of mastitis (SCM) is more common and thought to cause more economic losses to the dairy industry. The current study aimed to investigate the prevalence, risk factors of SCM, and effects on reproduction of dairy cows in major milk-producing areas of Sri Lanka. A total of 1,357 cows of selected farms in 3 regions were examined in the study. California Mastitis Test was conducted for individual cows, and a score of 2 or more for any quarter without any clinical symptoms and abnormalities in milk was considered as positive for SCM. Samples from infected animals were collected and subjected to bacteriological analysis. A pretested questionnaire was used to collect data on individual cows and herds. Risk factors associated with SCM were analyzed using binary logistic regression in generalized linear mixed models. The effect of SCM on calving to conception interval and days from calving to artificial insemination were analyzed by survival analysis using Cox's proportional hazards regression and Kaplan-Meier survival function estimates, respectively. A Poisson regression model was run to determine the effect of SCM on number of artificial inseminations per conception. The prevalence of SCM was 57.5, 11.8, and 45.5% in the regions A, B, and C, respectively. The most common pathogen was Staphylococcus aureus, with 87.1, 56.5, and 92.3% in the regions A, B, and C, respectively. Logistic regression analysis showed that parity, farming system, milking area, region, and herd significantly affect the prevalence of SCM. Subclinical mastitis during the pre-breeding period was associated with 14% increase in the chance of having a greater number of artificial inseminations per conception. Likewise, median days from calving to artificial insemination was longer in cows with SCM compared with normal cows (79 and 64 d, respectively). Therefore, SCM affected the inseminated proportion of studied cows. However, SCM was not associated with the calving to conception interval. The results revealed that the cow factors and milk hygiene play a significant role in the prevalence of SCM.

Responses of Sri Lankan indigenous goats and their Jamnapari crosses to artificial challenge with Haemonchus contortus.

Goat farming plays an important role in the Sri Lankan rural economy. Sri Lankan indigenous (SLI) goats and their crossbreds are reared mainly under extensive management and indiscriminately exposed to pathogens and parasites. This study was designed to evaluate resistance to haemonchosis in SLI goats and their Jamnapari crossbreds (JCB) in the dry zone of Sri Lanka. Twenty SLI and 20 JCB 4-month-old male goats were artificially challenged with 5000 H. contortus L3 larvae. Faecal egg counts (FEC), body weights, FAffa MAlan CHArt (FAMACHA®) scores, packed cell volumes (PCV), red blood cell counts, total and differential white blood cell counts, blood haemoglobin contents, serum total protein and albumin contents, and serum pepsinogen and antibody levels were determined at 0, 21, 28, 35 and 42days after challenge. Effects of measurement time were significant for all variables (P<0.05). Breed effects approached significance (P=0.06) and measurement time×breed interaction was significant (P<0.05) for FEC. Peak FEC occurred at day 35 in both goat types, and JCB goats had higher FEC than SLI goats at days 28 (P<0.001), 35 (P<0.10), and 42 (P<0.10). Means for FEC at day 35 were 1783±446 eggs per gram of feces (epg) for SLI kids and 3329±850 epg for JCB kids. Haematological parameters, serum chemistry, and FAMACHA scores suggested that SLI goats were recovering from parasitic infection by day 42, whereas JCB goats had increasing severity of anaemia. Means for PCV in SLI goats decreased from 26.8±0.7% at day 0 to 19.7±0.9% at day 35 and thereafter increased to 20.2±0.9% at day 42. Means for PCV in JCB goats declined from 25.9±0.6% at day 0 to 17.2±0.9% at day 42. Eosinophilia was observed in both genotypes. The JCB goats were heavier than SLI goats and had higher antibody titres, reflecting higher levels of parasitism. Both goat types significantly increased in body weight during the experiment and therefore tolerated parasite infection without severe production losses. We concluded that SLI goats were more resistant to haemonchosis than JCB goats, but that JCB goats were somewhat resilient to parasitic infection. Substantial variability in measurements associated with parasite infection in both breeds indicated potential to improve parasite resistance. Phenotypic information should be coupled with genomic information to identify appropriate breeding goals for future selection programs.

Characteristics of prolonged luteal phase identified by milk progesterone concentrations and its effects on reproductive performance in Holstein cows.

A database of milk progesterone profiles consisting 497 lactations in 3 dairy herds from northern and western regions of Japan was used to identify the characteristics and associated risk factors for prolonged luteal phase (PLP) and its effects on subsequent reproductive performance in high-producing Holstein cows. Milk samples were collected twice weekly and progesterone concentrations in whole milk were determined by ELISA. Herds were visited monthly and examined by vaginoscopy and transrectal palpation. Resumption of ovarian cyclicity within 35 d postpartum followed by regular cycles was considered normal. Prolonged luteal phase was defined when progesterone concentrations were ≥5 ng/mL for ≥20 d of duration in any cycle postpartum. Delay of first ovulation to 35 to 60 d (delayed first ovulation type I), >60 d (delayed first ovulation type II), a luteal phase of <14 d except in the first cycle (short luteal phase), and the absence of luteal activity >14 d between 2 cycles (cessation of cyclicity) were the other categories of abnormal ovarian resumptions considered. The overall incidence of PLP in the 3 herds was 11.9% and a significantly higher proportion of PLP was observed in the first cycle postpartum compared with the second and third cycles. Approximately 83% of the PLP were 20 to 28 d in duration, and maximum progesterone concentration was significantly higher when PLP lasted >35 d compared with PLP of 20 to 35 d in duration. Higher parity, commencement of luteal activity≤28 d postpartum, and postpartum complications significantly increased the occurrence of PLP within 90 d postpartum. Cows with PLP showed reduced conception rate to first artificial insemination (AI) and reduced pregnancy proportions within 100, 150, and 210 d postpartum. Based on survival analysis, PLP was associated with a 56% reduction in relative pregnancy rate and a 36% reduction in AI submission rate. Cows that experienced PLP had a longer interval from calving to first AI (74 d) and from calving to pregnancy (141 d) than cows without PLP (53 and 80 d), respectively. In conclusion, 11.9% of lactations had PLP, of which approximately two-thirds were seen in the first cycle postpartum. Most of the PLP were 20 to 28 d in duration. Higher parity, postpartum complications, and early commencement of luteal activity postpartum increased the risk for PLP. Occurrence of PLP adversely affected fertility by reducing pregnancy proportions and extending calving to conception interval.

Modeling extended lactations of Holsteins.

Modeling extended lactations for the US Holsteins is useful because a majority (>55%) of the cows in the present population produce lactations longer than 305 d. In this study, 9 empirical and mechanistic models were compared for their suitability for modeling 305-d and 999-d lactations of US Holsteins. A pooled data set of 4,266,597 test-day yields from 427,657 (305-d complete) lactation records from the AIPL-USDA database was used for model fitting. The empirical models included Wood (WD), Wilmink (WIL), Rook (RK), monophasic (MONO), diphasic (DIPH), and lactation persistency (LPM) functions; Dijkstra (DJ), Pollott (POL), and new-multiphasic (MULT) models comprised the mechanistic counterparts. Each model was separately tested on 305-d (>280 days in milk) and 999-d (>800 days in milk) lactations for cows in first parity and those in third and greater parities. All models were found to produce a significant fit for all 4 scenarios (2 parity groups and 2 lactation lengths). However, the resulting parameter estimates for the 4 scenarios were different. All models except MONO, DIPH, and LPM yielded residuals with absolute values smaller than 2 kg for the entire period of the 305-d lactations. For the extended lactations, the prediction errors were larger. However, the RK, DJ, POL, and MULT models were able to predict daily yield within a +/- 3 kg range for the entire 999-d period. The POL and MULT models (having 6 and 12 parameters, respectively) produced the lowest mean square error and Bayesian information criteria values, although the differences from the other models were small. Conversely, POL and MULT were often associated with poor convergence and highly correlated, unreliable, or biologically atypical parameter estimates. Considering the computational problems of large mechanistic models and the relative predictive ability of the other models, smaller models such as RK, DJ, and WD were recommended as sufficient for modeling extended lactations unless mechanistic details on the extended curves are needed. The recommended models were also satisfactory in describing fat and protein yields of 305-d and 999-d lactations of all parities.

Productive life including all lactations and longer lactations with diminishing credits.

Alternative measures of productive life (PL) were compared, and life expectancy factors were updated to replace estimates from 1993. Alternatives were proposed with extra credits for lactations longer than 10 mo and beyond 84 mo of age and for each calving so that an extremely long lactation would not receive more credits than multiple shorter lactations with dry periods between. Maximum credits per lactation of 10 mo (original PL), 12 mo, and unlimited were compared. The unlimited credits option either included or excluded a calf value equal to 2 mo of production and had credits given for all days either uniformly or based on lactation curves (diminishing credits). Standard lactation curves (first, second, and greater lactations) were estimated based on the test-day yields of Holstein cows remaining in lactation from a set of 903,579 lactation records. For the diminishing credits alternative, credit for a given day of a parity was derived using the predicted yield of the day proportional to the average daily yield of the first 305 d of second parity. Daily yields were deviations from a baseline of 13.62 kg. Heritabilities and genetic correlations were estimated by multitrait REML for alternative measures of PL, for longevity censored at various ages, and for yield traits and SCS in first parity. Data for REML analysis included records from 1,098,329 Holsteins born from 1994 through 1997 from 5,109 sires, and a relationship matrix among sires was included in the model. Lactations beyond 84 mo added little information. Heritability of PL was 0.073 with 10 mo, 0.069 with 12 mo, 0.068 and 0.067 with unlimited (uniform) lactation credits (with and without calf credits, respectively), and 0.070 with unlimited diminishing credits. Corresponding correlations among predicted transmitting abilities for PL and protein yield were 0.07, 0.06, 0.12, 0.23, and 0.09, all much lower than the 0.46 estimated in 1993. Heritability of PL with diminishing credits improved from 0.017 to 0.070 when censoring age increased from 36 to 96 mo. There was no further increase in heritability beyond 96 mo. Genetic correlation with the final PL was 0.87 when PL was censored at 36 mo, but the estimate increased steadily with the censoring age. The PL with diminishing credits, which was favorable in both economic and genetic aspects, was desirable in crediting cows for complete lactations.

Pre-pubertal and postpartum anestrus in tropical Zebu cattle.

Bos indicus breeds, commonly known as Zebu cattle, have spread from their center of origin in Western Asia into large areas of Asia (including the Asia-Pacific basin), Africa, South and Central America (including the Caribbean islands). The original Zebu genotype, however, has been modified by planned and unplanned cross-breeding programs involving many native and Bos taurus breeds in their new habitats. Though accurate estimates are not available, more than half of the world's cattle population includes a proportion of B. indicus germ plasma. B. indicus native breeds have developed by natural selection over centuries for their ability to survive in rough, harsh tropical environments. Most of these non-described breeds still exhibit high fertility, in terms of calving rates, and disease resistance but they grow very slowly and take well over 3 years to reach puberty and produce only a few liters of milk over a short lactation period. Selection has been carried out in some areas and distinct Zebu breeds have been developed that have moderately high growth rate and milk production. However, they are slow breeders and have extended pre-pubertal and postpartum anestrous periods, compared to their temperate counterparts exposed to similar environment and management. The reproductive biology of B. indicus is similar to that of B. taurus. Most of the proven management, nutritional, hormonal and biotechnological interventions developed through experimentation with B. taurus breeds are equally applicable to B. indicus and their crosses. Zebu breeds predominate in most tropical countries where the majority of the human population lives. If meat and milk production are to be increased in the tropics, Zebu cow productivity, in terms of number of calves produced per lifetime or per unit area of land, must be increased and the time from birth to slaughter must be reduced. This goal could be achieved either by selection within local Zebu populations or through planned cross-breeding with B. taurus breeds. Because the productive and reproductive potentials of Zebu cattle are relatively low, worthwhile gains could only be achieved by selection over many generations. This would require substantial investment in labor, feed and drugs that may not be economic since the return from such investment is relatively low. However, many studies have shown that cross-breeding with B. taurus, which combines additive, dominance and epistatic effects of the two genotypes, ensures high productive and reproductive performance. Therefore, planned cross-breeding with suitable B. taurus breeds, although demanding additional investment in labor, feed and drugs, will still be economic because the return far exceeds the costs.