فهرس المقالات lactation curve

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  1 - Genetic Parameter Estimates for Lactation Curve Parameters, Milk Yield, Age at First Calving, Calving Interval and Somatic Cell Count in Holstein Cows
  A. Chegini A.A. Shadparvar N. Ghavi Hossein-Zadeh
  The objective of this study was to estimates the genetic and environmental components for the lactation curve parameters, milk yield, age at first calving (AFC), calving interval (CI) and somatic cell count (SCC) in Iranian Holstein cows. The dataset consisted of 210625 أکثر

  The objective of this study was to estimates the genetic and environmental components for the lactation curve parameters, milk yield, age at first calving (AFC), calving interval (CI) and somatic cell count (SCC) in Iranian Holstein cows. The dataset consisted of 210625 test day records from 25883 cows with milk yield in the first parity recorded from July 2002 to September 2007 in a total of 97 herds in Iran. The lactation curve and the selected lactation parameters were the scaling factor to represent yield at the beginning of lactation (a), the factor associated with the inclining (b) and declining (c) slopes of the lactation curves and the first 100-day milk yield, second 100-day milk yield, third 100-day milk yield, peak yield (Ymax), days in milk at peak yield (b/c), persistency (s), lactation length (LL) and the 305-day milk yield. The incomplete gamma function (Wood function) was used to estimate lactation curve and lactation parameters from daily milk records. Among the 100-day milk yield periods, the second 100-day milk yield had the highest heritability (0.29±0.024) and the highest genetic correlation with the 305-day milk yield (0.996±0.00). Lactation curve parameters had low h2 (0.017±0.007 to 0.051±0.011). The b / c had a relatively high genetic correlation with the 305-day milk yield (0.52±0.08), a moderate genetic correlation with CI (0.32±0.14) and negative genetic correlations with measures of somatic cell count. This suggested that b / c could be used as a criterion to improve 305-day milk yield and resistance to subclinical mastitis. تفاصيل المقالة
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  2 - Evaluation of Various Approaches in Prediction of Daily and Lactation Yields of Milk and Fat Using Statistical Models in Iranian Primiparous Holstein Dairy Cows
  M. Elahi Torshizi M. Hosseinpour Mashhadi
  In this research, 272977 test day records collected from 659 herds during years 2001 to 2011 by the Iranian animal breeding center were used. In the first section the ability of different models to predict daily milk yield from alternative milk recording was tested. The أکثر

  In this research, 272977 test day records collected from 659 herds during years 2001 to 2011 by the Iranian animal breeding center were used. In the first section the ability of different models to predict daily milk yield from alternative milk recording was tested. The result showed that a complex model including noon milking time plus the effect of lactation curve of Ali and Schaeffer function is the best equation for prediction of daily milk yield. The highest correlation between true and estimated daily milk yield (0.892) and the lowest bias (2.391) were obtained using this method. Of the four models, the Ali and Schaeffer and the Wood models resulted in the best goodness of fit and gave a good description of the lactation curve (milk and fat yield) for dairy herds when test-day yield is used. Lastly, the most appropriate models for prediction of 305 d milk and fat yields were Ali and Schaeffer and Wood respectively. These models were able to predict milk and fat yields with the lowest residual mean square errors. Thus, the performance of models based on lactation curve functions were better than the test-interval method and the centering date method for prediction of 305-d milk and fat yield in Iranian primiparous Holstein cows. تفاصيل المقالة
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  3 - Association of Birth Type and Pregnancy Type with Lactation Performance and Lactation Curve in Holstein Dairy Cows in Iran
  ه. آتشی م. دادپسند م.ج. ضمیری ا. اسعدی
  The association of birth type (single vs. double) and pregnancy type (single vs. double) with lactation performance and lactation curve was investigated in Holstein cows in Iran. Data of 243298 lactations on 138021 cows in 261 herds collected during January 2000 to Dece أکثر

  The association of birth type (single vs. double) and pregnancy type (single vs. double) with lactation performance and lactation curve was investigated in Holstein cows in Iran. Data of 243298 lactations on 138021 cows in 261 herds collected during January 2000 to December 2012 were used. The average twinning rate was 3.64% and ranged from 1.44% (primiparous) to 5.41% (multiparous). Factors associated with twining were calving season, calving year, herd, and parity. The rate of twinning increased from 2.49% in 2000 to 3.42% in 2012. The probability of twinning was higher in multiparous cows than that in primiparous [Odds ratio (OR) (95% confidence interval (CI))= 3.64 (3.44-3.84) for multiparous vs. primiparous cows]. The probability of twin pregnancy was higher in cows previously delivering twins than that in those delivering singles [OR (95% CI)= 3.17 (3.02-3.34) for cows delivering twins vs. cows delivering singles]. The lactation curve for cows delivering singles in previous gestation and pregnant with twins in subsequent gestation tended to be lower and flatter. The incidence of twin pregnancy was increased as the cow reached its peak yield earlier, and produced more milk at peak lactation. Primiparous cows delivering singletons in their previous gestation and having twins in their subsequent gestation produced more 100-d, 200-d and 305-d milk than those pregnant with singletons. Multiparous cows that delivered singleton in previous gestation and were pregnant with twin in the subsequent gestation, produced more milk during the first 100-d and 200-d of lactation than those pregnant with singles. تفاصيل المقالة
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  4 - Effect of Milking Frequency on the Lactation Performance and Lactation Curve of Holstein Dairy Cows in Iran
  هـ. آتشی
  The aim of this study was to investigate the effect of milking frequency (three times daily vs. two times daily) on the lactation curve shape, partial and 305-d lactation performance in Holstein dairy cows in Iran. Data from February 2000 to December 2012 comprising 217 أکثر

  The aim of this study was to investigate the effect of milking frequency (three times daily vs. two times daily) on the lactation curve shape, partial and 305-d lactation performance in Holstein dairy cows in Iran. Data from February 2000 to December 2012 comprising 217345 lactations on 141364 cows distributed in 324 herds collected by the Animal Breeding Center of Iran were used. The mean milking frequency was 2.88 (0.32) times and increased from 2.72 (0.004) times in 2000 to 2.97 (0.002) times in 2012. The shape of the lactation curve for cows milked thrice daily tended to be higher and flatter than that for those milked twice. The first parity cows milked twice daily had a significant lower days in milk (DIM) until peak (79.52 (0.49) days) than those milked thrice (88.66 (0.28) days). In all parities except for parity ≥ 4, lactation persistency was higher in the cows milked thrice daily than in those milked twice. The percentages of increase in 305-d milk yield due to increasing milking frequency from two times to three times daily, were 12.34, 14.02, 12.79 and 14.76% for cows in parity 1 to parity ≥ 4, respectively. The 305-d milk yield was higher by 959 (28.89), 1175 (32.7), 1099 (38.6) and 1271 (45.0) kg for cows milked thrice daily than those milked twice in parity 1 to parity ≥ 4, respectively. The corresponding values for the 305-d fat yield were 4.35 (0.98), 16.68 (1.11), 17.19 (1.28) and 18.76 (1.51) kg. Based on the results of this study, it can be concluded that increasing milking frequency not only increased milk yield but also improved the initial yield, peak yield and lactation persistency. تفاصيل المقالة
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  5 - Estimation of Genetic Parameters for Lactation Curve Traits in Holstein Dairy Cows in Iran
  ف. سقانژاد ه. آتشی م. دادپسند م.ج. ضمیری ف. شکری-سنگری
  The objectives were to estimate (co)variance components and genetic parameters for lactation curve traits in Holstein dairy cows in Iran. The used data were records on Holstein cows collected during January 2003 to December 2012 by the Animal Breeding Center of Iran (Ka أکثر

  The objectives were to estimate (co)variance components and genetic parameters for lactation curve traits in Holstein dairy cows in Iran. The used data were records on Holstein cows collected during January 2003 to December 2012 by the Animal Breeding Center of Iran (Karaj, Iran). In order to describe the lactation curve, an incomplete gamma function was fitted to 691200 test-day records on 96263 lactations, 377696 test-day records on 52168 lactations, and 182143 test-day records on 24951 lactations for the first three parities, respectively. Lactation curve traits that were analyzed included a scaling factor associated with initial yield, the inclining and declining slopes of the curve, peak time, peak yield, 305-d milk yield and a lactation persistency measure derived from the incomplete gamma function. The estimated heritability of lactation curve traits for the first, second and third lactation ranged from 0.012 to 0.29, 0.017 to 0.15, and 0.02 to 0.13, respectively. Genetic correlations among lactation curve traits for the first, second and third lactation ranged from -0.68 to 0.99, -0.84 to 0.98 and -0.90 to 0.94, respectively. The estimated repeatability of lactation curve traits ranged from 0.07 to 0.40. The moderate to large positive genetic correlations of 305-d milk yield with initial yield, peak yield and lactation persistency suggest that one of these traits could be used as a selection criterion to improve all four traits. However, the peak yield and 305-d milk yield were more heritable than lactation were persistency and initial yield. تفاصيل المقالة
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  6 - The Application of Recursive Mixed Models for Estimating Genetic and Phenotypic Relationships between Calving Difficulty and Lactation Curve Traits in Iranian Holsteins: A Comparison with Standard Mixed Models
  م.س. مختاری م. مرادی شهربابک ا. نجاتی جوارمی گ.جی.ام روزا
  In the present study, records on 22872 first-parity Holsteins collected from 131 herds by the Animal Breeding and Improvement Center of Iran from 1995 to 2014 were considered to estimate genetic and phenotypic relationships between calving difficulty (CD) and the lactat أکثر

  In the present study, records on 22872 first-parity Holsteins collected from 131 herds by the Animal Breeding and Improvement Center of Iran from 1995 to 2014 were considered to estimate genetic and phenotypic relationships between calving difficulty (CD) and the lactation curve traits, including initial milk yield (Ap), ascending (Bp) and descending (Cp) slope of the lactation curves, peak milk yield (Ym), days to attain peak yield (Tm) and milk persistency (Pers) under recursive mixed models (RMMs) and standard mixed models (SMMs). Recursive mixed models (RMMs) were applied by fitting CD as a covariate for any of the studied lactation curve traits while considering genetic relationships between CD and these traits. The obtained results denoted a statistically significant non-zero magnitude of the causal relationships of CD with Ap and Bp, while the former influencing the latter. The causal effects of CD on Ap and were -0.351 kg and 0.005, respectively. Direct genetic correlations between CD and the studied traits under RMMs and standard mixed models (SMMs) were not statistically different from zero, except for the correlations of CD with Tm; indicating that genes associated with difficult births also increase peak days in milk. Comparison of both models by the deviance information criterion (DIC) demonstrated the plausibility of RMMs over SMMs for studying the relationships of CD with Ap and Bp while SMMs performed better for estimating the relationships of CD with Cp, Ym, Tm and Pers. تفاصيل المقالة
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  7 - Comparison of Different Lactation Curve Models to Describe Lactation Curve in Moroccan Holstein-Friesian Dairy Cows
  I. Boujenane
  In this study, the incomplete gamma function, an exponential function, a mixed-log function and a polynomial function were evaluated to describe the lactation curve in Moroccan Holstein-Friesian dairy cows. Data from 1990 to 1999, comprising 77130 monthly milk yields of أکثر

  In this study, the incomplete gamma function, an exponential function, a mixed-log function and a polynomial function were evaluated to describe the lactation curve in Moroccan Holstein-Friesian dairy cows. Data from 1990 to 1999, comprising 77130 monthly milk yields of 6029 dairy cows in 280 dairy herds, were used. Edits were carried out by considering the lactation length (5 d and تفاصيل المقالة