2.1 Data

The productive and genealogical records used come from the Limousin genetic evaluation database of the sclu-fvet-inia agreement.

The analyzed characteristics were weight at birth (wb), weight at weaning (ww), weight at 18 months (W18), ribeye area (rea) and rib fat thickness (rft) of bulls and heifers born between 2012 and 2016, belonging to four herds.

The data edition consisted of eliminating animals without date of birth and animals that received management based on natural field + ration, or pasture + ration. In turn, outlier records (less than 0.5% of the data) for W18 (>510 kg) and rib fat thickness (>8 mm) were deleted. Animals with weaning ages between 120 and 300 days were included for the characteristic ww (limits established for the national genetic evaluation), and for W18, animals of 457 to 640 days of age were included (18 months ± 3 months). The edition was carried out using the statistical program sas⁹.

2.2 Statistical analysis

Descriptive statistics of environmental effects were performed using the means procedure of the statistical program sas⁹. The effects of sex, herd, year of birth, management code, mother's age at parity, age at weaning, and age at 18 months were analyzed.

The study of the fixed effects on growth and carcass quality was carried out with the following model:

Regarding ww, the calf's age at weaning was included in the model as a covariate, and for w18, rea and rft the covariate age at 18 months. Possible interactions between effects were not considered due to the small number of records.

The analysis of fixed environmental effects included in the model was performed using the glm procedure of the statistical program sas⁹.

2.3 Connectedness

The study of connectedness between herds and years considered the same data as the analysis of environmental effects, and had information about the reference parents used.

The program conexf90¹⁰ was used to determine pevd and cr, considering weaning weight data grouped by year and cg, and assuming a heritability value of 0.30 for this characteristic according to the studies presented by Gregory and others¹¹, and Phocas and Laloë¹².

3.1 Environmental effects

The results of the descriptive statistics (Table 1) presented differences between males and females for all the characteristics, resulting in significant differences (p <0.05) for the characteristics, except for rft. The results of the model for growth and carcass quality are presented in Table 2.

Table 1: Descriptive statistics of the sex effect for the characteristics: birth weight, weaning weight, weight at 18 months, ribeye area, and rib fat thickness. 

Table 2: Variance analysis for birth weight, weaning weight, weight at 18 months, ribeye area (rea), and rib fat thickness (rft) of Limousin animals. 

The sex effect presented a significative value for the characteristics: wb, ww, w18 and rea, which coincides with the results of Simcic and others¹³, that worked with 167 Limousin animals, and Koch and Clark¹⁴, who with 5952 Hereford breed animals obtained that males were 1.2 kg and 11.8 kg heavier than females at birth and at weaning, respectively. Goldberg and Ravagnolo¹⁵, with Angus animals in Uruguay, found that the effects herd, year, and month of measurement of the characteristic were significant for the characteristics wb, ww, and w18. In this study with the Limousin breed, the herd and year effects significantly influenced all the characteristics, except for the herd effect for rft.

For their part, the Limousin calves born from 6 and 9-year-old mothers in this study were 1.9 kg (p<0.05) and 2.7 kg (p<0.01) heavier at birth than those from 2 to 4-year-olds, respectively. Meanwhile, 5, 7, and 8-year-old mothers had heavier calves at birth, but the differences were not significant with respect to 2 to 4-year-olds. Krupa and others¹⁶ reported similar results with various breeds, where 5 to 7-year-old mothers delivered the heaviest calves at birth. Koch and Clark¹⁴ obtained higher wb and ww in calves born to 3 to 6-year-old mothers. The inclusion in this work of a category of mothers where mothers with different ages were grouped because they did not have a date of birth could explain the differences with these authors.

The management effect was not significant to growth characteristics (wb, ww, and w18), which was striking given the differences in animal performance normally observed nationally when natural field, natural field and pasture, and only pasture managements are applied in the conditions of our country.

Weaning age covariate was significant for ww, where for each day animals presented 0.48 kg more at weaning (p <0.001), while covariate age at 18 months did not present statistical significance for w18, rea and rft.

3.2 Connectedness

From the information of the sires used by the herds and the effective offspring obtained in each herd, they were directly and/or indirectly connected only in the years 2013, 2014 and 2015. For 2012 there were only two herds, which were connected by a single parent. The number of sires used in common for the remaining years was three to four, with an average of six offspring per herd. In 2016, three herds were connected through two parents in common.

The average, minimum and maximum values of pevd of a herd with the others were 113.9, 27.8, and 354.3, respectively. Lower values of pevd would indicate a greater connectivity ranking between herds. pevd values from 2012 to 2016 tend to the reduction of these towards this last year (Table 3).

Table 3 shows pevd values and the connectedness rating (cr) between herds. The correlation between cr and pevd is -0.45¹⁷. The average, minimum and maximum values of cr of a herd with the other herds were 7.9, 0.03 and 58.6, respectively.

Table 3: Number of animals, minimum, maximum and herd which presents the highest connectivity ranking (cr), and prediction error variance average (pevd) per herd and year. 

There are few references to cr values in the literature. Mathur and others⁸ worked with rear fat thickness in swines, and propose a connectivity ranking greater than 3%, as an acceptable cr value. Considering that value as a reference, the A, B, and C Limousin herds for 2016 have an acceptable degree of connectedness between them.

For their part, Roso and others¹⁷ studied different methods of measuring connectivity in bulls from a Canadian testing center They obtained an average value of pevd of 1726 between a group of animals and the rest, and a cr of 1.2%. Regarding the work carried out with the Limousin breed in Uruguay, the results are different for both measures, since average values of 113.9 and 7.9% were obtained for pevd and cr, respectively.

The results could be explained by the small size of the contemporary groups considered in the study since, as mentioned by Mathur and others⁸, it is recommended that the gc have at least ten animals and three different parents to obtain adequate connectedness values. Roso and others¹⁷ state that a group evaluated with few parents presents a greater variation in the pevd and cr, which indicates a greater variation in the degree of connectedness between groups. It is important to note that the smaller the number of animals per group, the pevd increases and the cr decreases.

Based on what was presented, the herds participating in the genetic evaluations of the Limousin breed for the evaluated years were directly and/or indirectly connected, but with low connectivity values (less than 3% of cr proposed by Mathur and others⁸) that did not yet warrant a population genetic evaluation.