PHENOTYPIC AND GENETIC CORRELATIONS BETWEEN FIRST LACTATION MILK YIELD AND SOME PERFORMANCE TRAITS IN SAHIWAL CATTLE

Data on 8948 pedigree, breeding and performance records of a purebred herd of Sahiwal cattle maintained at the Livestock Experiment Station Jahangirabad district Khanewal (Pakistan) during the period 1939-98 were analysed. The phenotypic, genetic and residual correlations between first lactation milk yield and some first lactation and lifetime traits were estimated, using Bivariate REML analysis. Phenotypic, genetic and residual correlations between first lactation milk yield and age at first calving were 0.67, 0.61 ± 0.30 and 0.73; between first lactation milk yield and first lactation length were 0.35, 0.48 ± 0.38 and 0.31; between first lactation milk yield and first calving interval were 0.39, 0.46 ± 0.46 and 0.39; between first lactation milk yield and first dry period were 0.35, 0.49 ± 0.46 and 0.30; between first lactation milk yield and lifetime milk yield were 0.02, 0.01 ± 0.77 and 0.05. Positive and high genetic correlation between first lactation milk yield and age at first calving indicated that the selection for higher first lactation milk yield would increase the age at first calving, which is not advantageous

Phenotypic effects of calving ease on the subsequent fertility and milk production of dam and calf in UK Holstein-Friesian heifers

The effect of calving ease on the fertility and production performance of both dam and calf was studied in approximately 50,000 and 10,000 UK Holstein-Friesian heifers and heifer calves, respectively. The first objective of this study was to estimate the effect of a difficult calving on the subsequent first-lactation milk production by estimating lactation curves using cubic splines. This methodology allows the estimation of daily milk, protein, and fat yields following calvings of differing degrees of difficulty. Losses in milk yield after a difficult calving have been quantified previously; however, estimates are generally restricted to the accumulated yields at specific days in lactation. By fitting cubic splines, gaps (in which the shape of the lactation curve can be merely guessed) between estimations were avoided. The second objective of this study was to estimate the effect of a difficult birth on the subsequent performance of the calf as an adult animal. Even though the calving process is known to involve cooperation between dam and calf, the effect of a difficult calving has, until now, only been estimated for the subsequent performance of the dam. Addressing the effects of a difficult birth on the adult calf strengthens the importance of calving ease as a selection trait because it suggests that the benefit of genetic improvement may currently be underestimated. The effect of calving ease on the subsequent reproductive performance of dam and calf was analyzed using linear regression and with calving ease score fitted as a fixed effect. Dams with veterinary-assisted calvings required 0.7 more services to conception and 8 more days to first service and experienced a 28-d longer calving interval in first lactation compared with dams that were not assisted at calving. Effects of calving ease on the reproductive performance of the adult calf in first lactation were not detected. Losses in milk yield of the dam were significant between d 9 to 90 in milk subsequent to a veterinary-assisted calving, creating a loss of approximately 2kg of milk per day, compared with a nonassisted calving. Calves being born with difficulties showed a significant reduction in milk yield in first lactation, demonstrating the lifelong effect of a difficult birth. Compared with nonassisted calves, veterinary-assisted calves showed a loss of 710kg in accumulated 305-d milk yield, which was significant from 129 to 261 d in milk. This suggests that from birth to production, physiological effects of a bad calving are not negated. Results furthermore suggest a beneficial effect of farmer assistance at calving on the milk yield of both dam and calf, when moderate difficulties occurred

Milk production and survival of spring-calving carryover cows in New Zealand dairy herds : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Manawatu, New Zealand

Non-pregnant cows are generally culled from dairy herds and replaced with two-year-old heifers. Alternatively, non-pregnant cows can be dried-off at the end of lactation, retained for one year (carried over), before being mated and returned to a milking herd in the following year. In this study, calving interval was used as a tool to identify and define the carryover cow population in spring-calving dairy herds. Linear modelling methods were used to compare carryover cow milk production with that of heifers, lactation-matched and age-matched non-carryover cows. Lastly, the survival for second-lactation carryover cows was compared with that of two-year-old heifers and lactation-matched non-carryover cows. Results showed that annually, 2.5% of spring-calving cows had returned to a milking herd after a carryover period in the previous year. Of those carryover cows, 43% returned to a milking herd at four years old, after failing to conceive in their first lactation. Most (69%) dairy herds contained less than 5% carryover cows and 17% of dairy herds comprised of zero carryover cows. The difference between the proportion of Holstein-Friesian in the carryover cow and non-carryover cow group was minimal (2%) but statistically greater (P<0.01) for the carryover cow group. Estimated breeding values (EBVs) for milk traits (milk yield, fat yield, protein yield and somatic cell count) were greater (P<0.01), but fertility EBVs were lower (P<0.01) for the carryover cow group in the year when they failed to conceive, compared to those for the non-carryover cow group. These were reflected in greater (P<0.01) selection indices (Breeding Worth and Production Worth) for carryover cows. After the carryover period, EBVs for milk traits and fertility decreased, and Breeding Worth was lower (P<0.01) for the carryover cow group, compared to the non-carryover cow group. Carryover cow milk yield, fat yield, protein yield and somatic cell score was greater (P<0.01) than those for heifers, lactation-matched and age-matched non-carryover cows in their first carryover year. This milk production advantage was maintained for up to three carryover years, if the carryover cow maintained an annual calving pattern, but at a decreasing rate. The probability of survival (days) was lower (P<0.01) for second-lactation carryover cows when compared to heifers and lactation-matched non-carryover cows. These findings are important for the New Zealand dairy industry as they can aid on-farm culling (removal from the herd) decisions

Prenatal maternal effects on body condition score, female fertility, and milk yield of dairy cows

In this study, maternal effects were described as age of dam at first and second calving, first-lactation body condition score (BCS) of the dam during gestation, and milk yield of the dam. The impact of these effects on first-lactation daughter BCS, fertility, and test-day milk yield was assessed. The effect of milk yield of dam on daughter 305-d yield in the latter's first 3 lactations was also investigated. The proportion of total phenotypic variance in daughter traits accounted for by maternal effects was calculated. Dams calving early for the first time (18 to 23 mo of age) had daughters that produced 4.5% more first-lactation daily milk, had 7% higher BCS, and had their first service 3 d earlier than cows whose dams calved late (30 to 36 mo). However, daughters of dams that calved early had difficulties conceiving as they needed 7% more inseminations and had a 7.5% higher return rate. Cows from second calvings of relatively young (36 to 41 mo) dams produced 6% more first-lactation daily milk, had 2% higher BCS, and showed a significantly better fertility profile than cows whose dams calved at a late age (47 to 55 mo) High maternal BCS during gestation had a favorable effect on daughter BCS, nonreturn rate, and number of inseminations per conception. However, it was also associated with a small decrease in daughter daily milk yield. Changes in dam BCS during gestation did not affect daughter performance significantly. Maternal effects of milk yield of the dam, expressed as her permanent environment during lactation, adversely affected daughter 305-d milk, fat, and protein yield. However, although the effect was significant, it was practically negligible (&lt;0.3% of the mean). Finally, overall maternal effects accounted for a significant proportion of the total phenotypic variance of calving interval (1.4 +/- 0.6%) and nonreturn rate (1.1 +/- 0.5%).</p

Fitting lactation curves of dairy cattle in different types of herds in Tunisia

peer reviewedThe incomplete gamma function was used to fit lactation curves of Holstein-Friesian cows in four types of herds in Tunisia. A total of 8640 records were used in the analysis. These included 1269, 637, 239, and 498 first lactation and 2986, 1441, 650, and 920 second and later lactation records in four herd groups namely investors, state, cooperative, and farmers' herds, respectively. The effects of environmental variables, production sector, herd, parity, first test-day date, calving year, and calving season on the main lactation curve traits were analysed. The factors associated with milk yield at the beginning of lactation and the decreasing phase of the curve, persistency, and peak yield varied significantly (P<0.01) with all variables. The ascending phase of the lactation curve was not affected by parity and calving year, while days in milk until peak depended only on the rank of lactation. The state herds had the lowest peak and total yields. The summer season was unfavourable for milk production. In contrast to first lactation cows, third lactation cows had the highest peak and total yields. Milk yield was highly correlated with peak yield (r = 0.79) and was not related to persistency measure. (C) 2003 Elsevier B.V. All rights reserved

Modelling the lactation curve of dairy cows using the differentials of growth functions

Descriptions of entire lactations were investigated using six mathematical equations. comprising the differentials of four growth functions (logistic. Gompertz, Schumacher and Morgan) and two other equations (Wood and Dijkstra). The data contained monthly milk yield records from 70 first, 70 second and 75 third parity Iranian Holstein cows. Indicators of fit were model behavior, statistical evaluation and biologically meaningful parameter estimates and lactation features. Analysis of variance with equation, parity and their interaction as factors and with cows as replicates was performed to compare goodness of fit of the equations. The interaction of equation and parity was not significant for any statistics, which showed that there vas no tendency For one equation to fit a given parity better than other equations. Although model behaviour analysis showed better performance of growth functions than the Wood and Dijkstra equations in filling the individual lactation curves, statistical evaluation revealed that there was no significant difference between file goodness of fit of the different equations. Evaluation of lactation features showed that the Dijkstra equation was able to estimate the initial milk yield and peak yield more accurately than the other equations. Overall evaluation of the different equations demonstrated the potential of the differentials of simple empirical growth functions used in file Current study as equations for fitting monthly milk records of Holstein dairy cattle

Non-nutritional strategies to improve lactation persistency in dairy ewes

Milk production is largely dependent on the shape of the lactation curve. Important elements in the lactation pattern are the peak yield, which is the maximum milk yield during lactation, and lactation persistency, which is the ability of animals to maintain a reasonably constant milk yield after the lactation peak. "Persistent" animals are those with flatter lactation curves. Domesticated animals have lactation curves with high peaks and persistency, and thus higher milk yield than their wild ancestors. Dairy breeds, when compared to meat and wool breeds, have greater persistency rather than high peaks. In dairy sheep, genetic selection has caused deep morphological changes in the udder and physiological changes in the whole body of the animal. The former are seen in the higher mammary cistern volume and the latter in neuro-hormonal changes that allow the alveoli to have a longer life-span and maintain a metabolic status that favors the switch of energy and nutrients to the mammary gland instead of body reserves. In practice, the ideal lactation curve has a reasonably high peak and a flat trend after the peak. More persistent lactation is desirable due to the relationships between this trait and health status and feed costs (Dekkers et al., 1998; Grossman et al., 1999). Animals with very high peak yields are not able to consume adequate amounts of nutrients in the first part of lactation. This causes a negative energy balance, reduced reproductive efficiency and increased susceptibility to diseases (Jakobsen et al., 2002; Swalve, 2000). By contrast, animals with flat curves are less subject to metabolic stress in early lactation and have a more constant pattern of energy requirements throughout lactation. This means that cheaper feeds can be used (Sölkner and Fuchs, 1987; Dekkers et al., 1998). In most cases the milk of the first month of lactation is suckled by the lamb. This means that there is less milk yield data available on the ascending phase of lactation, which consequently has been little studied

Estimates of genetic and phenotypic parameters for dairy traits in Friesian-Bunaji crossbreds

Genetic and phenotypic parameters for dairy traits were computed using data on Friesian-Bunaji crossbred cows collected over a twenty-three year period (1967-1989) from the dairy herd of the National Animal Production Research Institute Shika, Zaria, Nigeria. Estimated repeatabilities computed from variance components were 0.72 ± 0.06,0.60 ± 0.10,0.73 ± 0.02,0.53 ± 0.24 and 0.56 ± 0.18 for total lactation yield, lactation length, 305-day yield, calving interval and dry period, respectively. Heritability estimates were 0.44 ± 0.07,0.52 ± 0.12,0.30 ± 0.13,0.18 ± 0.02,0.26 ± 0.08 and 0.27 ± 0.10 for total lactation yield, lactation length, 305-day yield, calving interval, dry period and age at first calving,respectively. Genetic and phenotypic correlation coefficients between traits were medium to high, ranging from 0.30 to 0.95. The results of this study showed that the genetic response to selection in Friesian-Bunaji crosses for total lactation yield, 305-day yield and lactation length could be moderately high since the proportion of additive genetic variance was fairly high. Improvement programmes for age at first calving, calving interval and dry period should focus mostly on management, given their low heritability estimates

Organic dairy cows: milk yield and lactation characteristics in thirteen established herds and development of a herd simulation model for organic milk production

As a consequence of organic standards and principles, organic dairy producers are frequently faced with a different set of management considerations than those found in conventional dairy systems. The broad objective of this study was to examine in detail the production characteristics of 13 well-established organic dairy herds, and to relate these to the specific conditions that exist within organic dairy farming. Monthly milk records for 13 organic herds for three years were collected and converted into a Microsoft Access database, using InterHerd™ (Agrisoft Plc., UK) herd management software. The data were sorted and analysed using the InterHerd-herd management, Excel for Windows™ and Statistix for Windows software programmes. Estimated parameters were used to examine the importance of two important indicators: lifetime yield/lactation length and economic efficiency. To assess the first, a spreadsheet model based on the Wood's lactation curve was developed. With regard to the latter, a model calculator was used. Five herds were chosen for case studies, that examined the farm performance by using InterHerd™-generated data and by interviewing the producer retrospectively and asking him to comment on the data. Results Milk yield and lactation characteristics The 13 established, organic herds were characterised with relatively low yields, but herd variation was great: from a total lactation yield of 5,100 kg to 7,000 kg. Milk fat and protein content, lactation length and individual cow SCC means were similar to those reported in conventional, milk recorded herds. Lactation yields increased up to the third lactation, whereas persistency of lactations decreased up to the third lactation. This pattern followed similar patterns reported in conventionally managed herds. Similarly, somatic cell counts increased with parity, mimicking similar phenomenon reported in conventionally managed dairy cows. Length of lactation and lactation persistency were associated with month of calving, with autumn calving cows tending to have shorter lactations with better persistency. This phenomenon was, however, confounded with parity. Fertility It is concluded that fertility performance in terms of culling for fertility and mean calving intervals were better in the organic survey herds when compared with existing data from conventionally managed UK dairy herds. Good fertility performance even in the highest yielding organically managed cows suggests that early lactation energy deficit may not be a major problem in these herds. It is also suggested that financial impact of high number of services per conception, as observed in majority of the survey herds, may be insignificant as the main losses caused by poor fertility are attributable to culling and prolonged calving intervals. Herd models Herd productivity indices were generated, using an existing model based on a measure of feed conversion efficiency at the herd level. The advantage of using this approach in the estimation of productivity is that it takes full account of the entire feed input to the system, including forage. The production index was closely and independently associated with yield and calving rate. Culling was not independently associated with the production index but once calving rate and lactation yield are taken into account, culling rate also becomes a significant factor. Case studies Case studies demonstrated the usefulness of recorded data analysis, using herd management software and observation of seasonally adjusted lactation curves to examine feeding management. In all five herds, apparent and reoccurring seasonal feeding and grazing management shortcomings were detected. Recommendations Further research would need to be carried out to establish financial consequences of poor fertility in organic systems with different milk pricing and cow values. Similarly, further research is needed to establish causes for high numbers of services per conception in these herds and to establish whether this phenomenon exists in other organically managed herds. The herd productivity calculator model (LPEC) showed to be a good and robust measure of productivity. Next logical step in this analysis would be to gain data on purchased feeds, so that the productivity index can be expressed in terms of a gross margin per unit of forage input. This would allow the full importance of forage to organic dairy systems to be expressed, and would also allow productivity to be evaluated in terms economic margin per unit of input produced on-farm. The LPEC generated indices could also be utilised to examine the potential impact of changes to systems before an intervention is implemented, by including costs of intervention and assumed values of production post-intervention. Sensitivity analyses may be conducted to identify the relative importance of individual production parameters to overall herd productivity. Careful assessment of lactation characteristics in a herd is needed to predict the overall impact of extended calving intervals. It is likely that in most organic herds feeding management would need to be adjusted in order to produce lactations with low late lactation decline to avoid financial losses caused by longer calving intervals. Analysis of seasonally adjusted lactation curves as a monitoring and decision support system for feeding management is likely to be a useful for organic herds, particularly during conversion period when new feeding systems need to be introduced in a herd

Organic versus conventional dairy farming – studies from the Öjebyn Project

This report was presented at the UK Organic Research 2002 Conference. A study (the Öjebyn Project) was conducted to determine differences between organic and conventional dairy farming systems. Comparisons of feed intake, milk production, live weight (LW), feed efficiency and animal health were conducted, based on records from 145 dairy cows (238 parities). A lower daily metabolisable energy (ME) intake, lower milk yield and a higher protein content were recorded in the organic herd during the first ten weeks of lactation. No differences were recorded between the systems in either average total DM intake or efficiency of feed conversion, calculated as MJ of feed/kg of energy-corrected milk (ECM). There were a trend to lower LW change and better health in the organic herd. Most differences between the systems were recorded during the early lactation period