Genetic improvement of meat sheep. 4. Effect of age of dam on productivity of Dorset and Border Leicester sheep

1977 ◽  
Vol 17 (88) ◽  
pp. 735 ◽  
Author(s):  
IP Gregory ◽  
EM Roberts ◽  
JW James
Keyword(s):  
Genetic Improvement ◽  
Weaning Weight ◽  
Maximum Productivity ◽  
Clear Association ◽  
Meat Sheep ◽  
Effect Of Age ◽  
Age Structures

The effect of age of the dam on the number of lambs born (LBL) and weaned (LwL) and the weight of lambs weaned (WLWL) per ewe lambing and on the number of lambs weaned per lamb born (LwB) and lamb weaning weight (WWT) has been estimated for Dorset and Border Leicester sheep. In both breeds, LBL, LWL and WLWL showed a clear association with age of the dam, rising to a peak at a dam age of five years in the Dorsets and at between four and six years in the Border Leicester. The association between age of dam and WWT and LWB was less marked. WWT rose to a peak in both breeds at a dam age of five years and LWB rose to a peak at four and three years in the Dorsets and Border Leicester respectively. The estimates of ewe productivity were used to calculate the productivity of Dorset flocks of differing age structures. It was found that maximum productivity would be achieved with a flock aged from two to six years.

Genetic improvement of meat sheep. 1. A comparison of different methods of correcting weaning weight for age of lamb

1976 ◽  
Vol 16 (80) ◽  
pp. 325 ◽  
Author(s):  
IP Gregory ◽  
EM Roberts ◽  
JW James
Keyword(s):  
Birth Weight ◽  
Genetic Improvement ◽  
Average Daily Gain ◽  
Weaning Weight ◽  
Significant Difference ◽  
Meat Sheep ◽  
Daily Gain ◽  
Weight For Age

Several methods of correcting lamb weaning weight for age were compared. Lambs were weighed at birth, at 90 � 1 day of age, when the oldest and when the youngest lamb was 90 days and when the average age of lambs was 90 days. Weights were adjusted to 90 days by the methods of regression, regression pooled within sire groups, average daily gain with and without a standard birth weight and weight per day of age. All the correction methods examined gave similar results and there was no significant difference between methods. The correlations between the actual 90-day weight and the adjusted weights ranged from 0.922 to 0.960 and were highest when the weights taken when the average age of lambs was 90 days were used as the basis for adjustment. All adjusted weights were significantly biased as estimates of actual 90-day weight, but the bias was least for weights when average age was 90 days.

Genetic improvement of meat sheep. 2. Correction of weaning weight in Dorset and Border Leicester sheep

1977 ◽  
Vol 17 (84) ◽  
pp. 31 ◽  
Author(s):  
IP Gregory ◽  
EM Roberts ◽  
JW James
Keyword(s):  
Environmental Factors ◽  
Least Squares ◽  
Genetic Improvement ◽  
Average Daily Gain ◽  
Regression Method ◽  
Least Squares Estimation ◽  
Weaning Weight ◽  
Meat Sheep ◽  
Daily Gain

Data from 14635 Dorset and 1214 Border Leicester lambs from nine properties and five years were used to estimate the effects on weaning weight of age of lamb, sex, birth-rearing status and parity of dam, using three methods (average daily gain, pooled regression and least squares). Corrections for all effects varied greatly over properties and years, indicating that weaning weight cannot be satisfactorily adjusted for these environmental factors by the use of standard corrections. The correlations between estimated effects from the three methods were significant, and correlations between the three adjusted weaning weights exceeded 0.9 in most cases. All three methods accounted for similar fractions of variance in weaning weight, but average daily gain correction actually increased the variance on some occasions. Since least squares estimation is complicated, it is concluded that the pooled regression method is better suited to performance recording applications, especially if corrections are estimated within weaning groups, as they should be in view of their variability.

Genetic improvement of meat sheep. 5. Heritability of post-weaning weight and gain in Dorset and Border Leicester sheep

1978 ◽  
Vol 18 (90) ◽  
pp. 63 ◽  
Author(s):  
IP Gregory ◽  
EM Roberts ◽  
JW James
Keyword(s):  
Body Weight ◽  
Genetic Improvement ◽  
Degrees Of Freedom ◽  
Sums Of Squares ◽  
Weaning Weight ◽  
Meat Sheep

The heritability of corrected post-weaning weight has been estimated for both Dorset and Border Leicester sheep and the heritability of corrected post-weaning gain and the repeatability of body weight for Dorset sheep. In the Dorsets, the half-sib heritabilities of corrected post-weaning weight were 0.36, 0.1 4 and 0.28 respectively for rams, ewes and pooled over sexes. The corresponding parent-offspring heritabilities were 0.17, 0.32 and 0.25 respectively. The half-sib heritabilities of corrected post-weaning gain were respectively 0.28, 0.21 and 0.32 and the corresponding parent-offspring estimates -0.31, 0.03 and -0.14. The repeatability of body weight was estimated as 0.64 for both sexes. In the Border Leicester, the half-sib heritability of corrected post-weaning weight was 0.26, 0.17 and 0.23 for rams, ewes and pooled over sexes respectively. The corresponding parent-offspring estimates were 0.09, 0.04 and 0.06. Heritabilities were estimated on a within-property basis and then pooled over properties. Two methods of pooling the half-sib heritabilities were compared: 1. pooling the sums of squares and cross products and degrees of freedom and 2, pooling by weighting each estimate by the inverse of its variance. Pooling by method 1. resulted in consistently higher estimates than did pooling by method 2. Reasons for this are discussed.

Genetic improvement of meat sheep. 3. Heritability of weaning weight of Dorset and Border Leicester sheep

1977 ◽  
Vol 17 (84) ◽  
pp. 38 ◽  
Author(s):  
IP Gregory ◽  
EM Roberts ◽  
JW James
Keyword(s):  
Least Squares ◽  
Genetic Improvement ◽  
Average Daily Gain ◽  
Weaning Weight ◽  
Significant Difference ◽  
Meat Sheep ◽  
Daily Gain

The heritability of weaning weight, uncorrected and corrected by three different methods has been estimated from several Dorset properties and one Border Leicester property. The estimates varied greatly over properties. The half-sib heritabilities of uncorrected weaning weight exceeded those of all corrected weights in all properties but one and the reason was found to be non-random use of sires over the joining period. The pooled half-sib heritabilities of uncorrected weaning weight and weaning weight corrected by average daily gain, pooled regression and least squares were 0.27, 0.11, 0.15 and 0.18 respectively for the Dorsets and the corresponding estimates for the Border Leicester were 0.46, 0.20, 0.15 and 0.16 respectively. In the Dorsets the pooled heritabilities calculated by dam-offspring regression were 0.04, 0.06, 0.09 and 0.10 for uncorrecred weaning weight and weaning weight corrected by average daily gain, pooled regression and least squares respectively. There was no significant difference between the heritabilities of weaning weight corrected by least squares or pooled regression but the heritability of weaning weight corrected by least squares significantly exceeded that of weaning weight corrected by average daily gain.

Milk production in Awassi and Hungarian Merino sheep in Iraq

1971 ◽  
Vol 76 (3) ◽  
pp. 507-511 ◽  
Author(s):  
H. A. Karam ◽  
K. H. Juma ◽  
M. Al-Shabibi ◽  
J. Eliya ◽  
H. N. Abu Al-Ma'ali
Keyword(s):  
Birth Weight ◽  
Correlation Coefficient ◽  
Milk Production ◽  
Milk Yield ◽  
Correlation Coefficients ◽  
Multiple Correlation Coefficient ◽  
Lactation Period ◽  
Weaning Weight ◽  
Stage Of Lactation ◽  
Effect Of Age

SUMMARYOn the Abu-Ghraib Experiment Station, milk production was investigated in 31 Awassi ewes of different ages and 12 newly imported Hungarian Merino ewes, two years old, together with the effect of age, lactation period, number of lambs born and reared and stage of lactation on milk production in the Awassi ewes. The relationships between milk production, birth weight and weaning weight of lambs were also investigated.First-lactation milk yield during the suckling period (90 days) based on 12 h milking interval was 114·58 kg in the Merino and 75·29 kg in the Awassi.Age had no significant effect on milk production in Awassi ewes although first-lactation yield was lower than that from subsequent lactations. Ewes that produced and nursed twins gave significantly more milk than ewes that produced and nursed single lambs.Milk yield in Merino and Awassi ewes increased with the decrease of milking interval from 12 to 4 h. The correlation coefficients between milk yield during 12 and 4 h were positive and significant.Correlation coefficients between birth and weaning weights and milk production were positive in both breeds. The correlation coefficient between weaning weight and milk production was 0·78 in the Awassi (P <0·01) and 0·65 in the Merino (P <0·05). The multiple correlation coefficient between weaning weight and birth weight and milk production was 0·67 in the Awassi and 0·43 in the Merino.

Estimation of environmental effects on post-weaning gain and yearling weight of beef cattle

1977 ◽  
Vol 17 (89) ◽  
pp. 885 ◽  
Author(s):  
WM Straw ◽  
LP Jones
Keyword(s):  
Beef Cattle ◽  
Environmental Effects ◽  
Season Of Birth ◽  
Weaning Weight ◽  
Cattle Herds ◽  
Effect Of Age

Records of post-weaning growth for 1134 heifers and 375 bulls from 11 Victorian beef cattle herds were analysed for the effects of sex, age of dam, age of calf, season of birth and herd/year on postweaning gain (PWG) and yearling weight (YLG WT). Age of dam had a significant effect on PWG and YLG WT for each sex, but the effect on heifer PWG was small. Suitable corrections for the effect of age of dam on heifer YLG WT were made using weaning weight adjusted for age of dam effects plus gain from weaning to yearling. Post-weaning management of young bulls and heifers was very different. Averaged over all herd/years, bulls were 37.5 per cent heavier than heifers at yearling age and grew 57.5 per cent faster between the two post-weaning dates, The environmental effects on PWG and YLG WT were therefore different for each sex. The effects of calf age and season were significant for each dependent variable except YLG WT for bulls and PWG for bulls respectively. The interaction between calf age and season was significant for heifers only.

Some components of reproductive performance of sheep in Victoria

1970 ◽  
Vol 21 (6) ◽  
pp. 945 ◽  
Author(s):  
PD Mullaney ◽  
GH Brown
Keyword(s):  
Reproductive Performance ◽  
Relative Number ◽  
Relative Contribution ◽  
Effect Of Age ◽  
Age Estimates ◽  
Age Structures

Estimates are given of the relative contribution of each component of reproductive performance - the relative number of ewes having no, one, or two lambs - in the effect of age on the number of lambs born per ewe joined for Merino and Corriedale sheep in Victoria. For Merinos, the proportion of ewes giving birth to more than one lamb increased by 0.05 from ages 3 to 6, followed by a decline of 0.02 at age 8. For Corriedales, this proportion increased by 0.06 from age 3 to age 6. The proportion of ewes having no lamb was greater at the maiden lambing (age 3, Merinos; age 2, Corriedales) than at any other age. Estimates of the effect of age on these components are used to assess the reproductive performance of flocks of different age structures.

ENVIRONMENTAL FACTORS AFFECTING PRE- AND POST-WEANING TRAITS OF HEREFORD BULL CALVES

1965 ◽  
Vol 45 (3) ◽  
pp. 189-195 ◽  
Author(s):  
T. D. Burgess ◽  
G. H. Bowman
Keyword(s):  
Average Daily Gain ◽  
Average Weight ◽  
Weaning Weight ◽  
Factors Affecting ◽  
Bull Calves ◽  
Population Average ◽  
Adjustment Factors ◽  
Good Environment ◽  
Daily Gain ◽  
Effect Of Age

Records of 1372 Hereford bull calves tested under the Ontario Advance Registry Policy for beef cattle were analyzed to estimate the effect of age of dam, season of birth, and year of birth on 240-day (weaning) weight, average daily gain (postweaning), and weight per day of age.Two- and three-year-old cows weaned calves 34.3 and 13.5 lb below the population average. As age of cow increased from 4 to 8 years little change occurred; however, older cows weaned calves 13.5 lb above average. Weight per day of age showed a trend identical with weaning weight. Age of cow did not influence postweaning growth. Calves born during the fall and winter weaned slightly heavier than those born during the spring and summer. Although certain trends were evident and differences were significant, less than 10% of the total sum of squares were partitioned by the combined effect of age of dam, season, and year. An appropriate set of adjustment factors based on the analysis would be provided by the addition of 40 and 15 lb respectively to the weaning weights of calves from 2- and 3-year-old cows, and of.12 lb to the weight per day of age of calves from 2-year-old cows. It is postulated that under good environment calves from older cows will grow as well as their contemporaries from cows of a middle-age group.

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