Production of two composite beef cattle herds of Zebu x Criollo Yacumeño and Charolais x Zebu x Criollo Yacumeño on floodable savanna in Beni, Bolivia
I. Weaning weights

D Plasse, B Bauer*, E Galdo* and O Verde

Universidad Central de Venezuela, Facultad de Ciencias Veterinarias, Maracay, Venezuela,
*Estancias Espíritu, La Paz, Bolivia
dplasse@intercable.net.ve

Abstract

The objective of this study was to evaluate three generations of weaning weights (WW) of calves produced by two composite herds founded in 1975 at a private ranch in Beni, Bolivia: Herd A with F₁ Zebu x Criollo cows and bulls and Herd B with 1/2Charolais1/4Zebu1/4Criollo, F₁ Zebu x Criollo and 3/4Zebu1/4Criollo cows bred to 1/2Charolais1/4Zebu1/4Criollo bulls. Both herds were maintained on floodable savanna and calves were weaned at 8 months.

Non-adjusted and least squares means for 8160 WW of Herd A were 177.4±0.3 and 175.1±0.7 kg at an age of 248±0.3 days and for 5654 weights of Herd B 174.5±0.4 and 174.0±0.8 kg at 250±0.3 days. Generation (G; n = 3) was an important (P<0.01) effect in Herd A but non-significant (P>0.05) in herd B. Sex (2), birth year (9), month of birth (5), age of dam in years (11), time of fasting (7 six-hour intervals) and age of calf (days, linear) were important (P<0.01) in both herds. Year x month was highly significant (P<0.01) in both herds and sex x year in Herd A (P<0.01) but not in B (P>0.05). Generation x sex was important (P<0.05) only in Herd A. WW of G₂ calves (offspring of foundation cows and bulls) in Herd A was highest and decreased 10.5 kg (6 %) in G₃. Herd A calves of G₂, G₃ and G₄ showed a 4.5, -2.5 and 0 % deviation from WW of Herd B calves.

While in Herd A F₁ cows weaned the heaviest calves and there was an important decrease of weights in G₃, in Herd B means of all three generations did not differ significantly. Adjusted means over all generations of both herds were similar. The mean adjusted WW of G₃ and G₄ of herds A and B did not show an advantage of economic importance over that published from the same ranch of a Zebu herd under selection.

Keywords: Beef cattle, composite herds, tropics, weaning weight

Resumen

El objetivo de este estudio fue evaluar el peso al destete (PD) de becerros producidos durante tres generaciones en dos rebaños compuestos fundados en 1975 en una estancia particular en Beni, Bolivia: Rebaño A con vacas y toros F₁ Cebú x Criollo y Rebaño B con vacas 1/2Charolais1/4Cebú1/4Criollo, F₁ Cebú x Criollo y 3/4Cebú1/4Criollo apareadas con toros 1/2Charolais1/4Cebú1/4Criollo. Ambos rebaños fueron mantenidos en sabana inundable y los becerros destetados a los 8 meses de edad.

Los promedios no ajustados y ajustados obtenidos por la técnica de cuadrados mínimos para 8160 PD del Rebaño A fueron 177.4±0.3 y 175.1±0.7 kg a una edad de 248±0.3 días y para 5654 pesos del Rebaño B fueron 174.5±0.4 y 174.0±0.8 kg a los 250±0.3 días. Generación (G; n =3) fue un efecto importante (P<0.01) en el Rebaño A, pero no significativo (P>0.05) en el Rebaño B. Sexo (2), año de nacimiento (9), mes de nacimiento (5), edad de la vaca en años (11), tiempo de ayuno (7 intervalos de 6 horas) y edad del becerro (días, lineal) resultaron importantes (P<0.01) en ambos rebaños. Año x mes fue altamente significativo (P<0.01) en ambos rebaños, mientras que sexo x año en el Rebaño A fue importante (P<0.01), pero no así en B (P>0.05). Generación x sexo fue importante (P<0.05) sólo en el Rebaño A. El PD de becerros de G₂ (progenie de vacas y toros de fundación) en Rebaño A fue el más alto y disminuyó en G₃ en 10.5 kg (6%). Los becerros del Rebaño A correspondientes a G₂, G₃ y G₄ señalaron una desviación de 4.5, -2.5 y 0% de los PD de los becerros del Rebaño B.

Mientras que en el Rebaño A las vacas F₁ destetaron los becerros más pesados y había una importante caída en los pesos en G₃, en el Rebaño B no se encontró una diferencia significativa entre las tres generaciones. Los promedios ajustados sobre todas las generaciones de ambos rebaños fueron similares. Los promedios ajustados de los PD de G₃ y G₄ de los rebaños A y B no tuvieron una ventaja de importancia económica sobre los publicados para un rebaño Cebú bajo selección en la misma estancia.

Palabras claves: Bovinos de carne, peso al destete, rebaños compuestos, trópico

Introduction

The floodable savannas of tropical South America, existing in Brazil (Pantanal), Colombia (Llanos), Venezuela (Llanos) and Bolivia (Beni), are of increasing interest for beef production from two reasons: (1) For most of their areas sustainable beef production systems seem to be the only realistic alternative to utilize these natural resources for human nutrition without endangering their ecological equilibrium and (2) beef produced from grass is favorable from the human health standpoint and production costs can be reasonable and may make this production system globally more competitive with stagnating or increasing cereal prices.

The ecosystem of floodable savannas of the Beni, Bolvia, includes about 11 millions of hectares and it appears that there is ample scope for increasing production in this area. The original cattle in the Beni are derived from different Bos taurus resources introduced by European missionaries in the XVII century. They were absorbed by Zebu introduced from different regions, mainly from Brazil, during the middle of the XX century. Today this process can be considered to have finished and only a few genetic resources of pure Criollo are still available, of which the Criollo Yacumeño is one of the most important (Bauer et al 1992; Verde et al 1993).

The upgrading process of Criollo to Zebu was evaluated at the ranch, where the present study was carried out (Bauer et al 1997; Plasse et al 1997) showing decreasing weights and reproductive efficiency after the very well performing F₁ - cow generation. A selected 600 cow Zebu herd and a selected 570 Criollo Yacumeño herd showed between 1967 and 1981 very similar production of weaning weight per cow in the herd (Bauer et al 1992; Galdo et al 1992; Plasse et al 1993; Verde et al 1993). Since heterosis values in Criollo x Zebu crossbreds had been reported to be of importance (revised in Plasse 1981, 1983) an experimental rotational crossbreeding program was carried out at another location in Beni and showed an advantage of the rotational crossbreds over grade Zebu of 7% for weight weaned per cow in the herd in advanced generations, while there was no advantage for final weight of steers (Galdo et al 2002; Plasse et al 2002a).

None of these results were in line with the exaggerated expectations about crossbreeding, typical of the last third of the past century. Rotational crossbreeding was complicated under extensive conditions. Therefore, in order to investigate another alternative, two composite herds were founded, one of 50% each of Zebu and Criollo breeding and the other of approximately 25% of genes from Charolais, 43% from Zebu and 32% from Criollo Yacumeño. The evaluation of the production of four generations of cows and three of calves of these two composite populations as an alternative to other breeding programmes carried out at this location, is the objective of the present series of two publications with the weaning weights being treated in this first part.

Materials and methods

The ranch at which the present study was realized is located at 15° S and 64° W along the Yacuma river, whose tributaries cross the floodable savanna. The area is characterized by a severe tropical climate. In normal years 80 to 90% of the ranch is flooded during the rainy season (October to March) and periodically severe floods require the evacuation of large areas and make routine work, like weaning, impossible. Severe droughts during the dry season (April to September) do also occur periodically. Mean temperature is 26.6° C (14 years average) and during the years of the experiment absolute minimum and maximum temperatures registered were 7° C and 39° C. Precipitation was 1865 mm on average of 20 years.

Three physiographic zones can be distinguished: (1) High areas well drained and not affected by floods, (2) semi - high or transition areas which might be flooded 5 to 40 cm and low areas with floods above 40 cm. Predominating native grass species of interest for beef cattle are in high areas Paspalum plicatum, Eleusine tristachya, Axonopus compressus and Cynodon dactylon. In transition areas main species are Panicum laxum, Leersia hexandra and Paspalum acuminatum. In low areas predominating grass species are Leersia hexandra, Hymenachne amplexicaulis and Paspalum fasciculatum (R Tejos, personal communication). A botanical description of the savanna of the area in which this ranch is locate has been given by Beck and Sanjinés 2005). At the time the present research was conducted, no cultivated pasture existed on the ranch. The adequate carrying capacity was about 0.25 AU ha^-1.

Two composite herds were founded. Herd A was composed of F₁ Zebu x Criollo (1Ze1Cr) cows and the same breed of bulls. The F₁'s had been produced out of commercial Criollo cows and Zebu bulls generated in a selected Zebu herd established in 1962 at the same ranch from Nelore-type Bos indicus cattle in which later on Brahman bulls were used. After 1964 a Criollo herd of 600 cows was also established, selected from 6000 commercial Criollo cows, later on named Criollo Yacumeño (Bauer et al 1992). Herd A was founded in 1975 and following years starting with 1063 1Ze1Cr cows, was closed in 1979 and maintained until 1988, when it reached 1745 cows.

Herd B was founded in 1975 with approximately 250 1/2Charolais1/4 Zebu1/4Criollo (2Ch1Ze1Cr) cows. In 1976, 250 1Ze1Cr cows and 350 3Ze1Cr cows were included. All cows were bred to 2Ch1Ze1Cr bulls. The 2Ch1Ze1Criollo cows had been produced by artificially breeding Charolais bulls to 1Ze1Cr cows. The herd was closed in 1978 with 879 cows and maintained until 1988, when it reached 1006 cows. Unfortunately no Zebu control group could be include in the design, however there was a Zebu herd kept on the same ranch from which published data were available for reference.

A maximum effort was made to keep herds A and B under similar environmental conditions. Calves were born in supervised calving pastures between June and October. They were immediately identified with birth year and individual number, dehorned and received basic health treatment. Although their mothers were known, their sires were not, because on this large ranch only multi - sire herds were used. Calves were maintained with their dams full time through weaning on native grass and weaned and weighed at 8 months of age in four monthly groups. Because of large distances and cattle numbers to be worked, calves were unavoidable fasted for a different length of time before weaning weight was taken. Therefore a fasting code was assigned to each calf differentiating seven 6 - hours intervals between 6 and 42 hours. Unusually heavy floods in 1977, 1981 and 1983, did not allow to weigh calves. Throughout their lives animals grazed native grass only and were offered common salt.

From the data files produced at the ranch, two data sets (herds A and B) were constructed after editing according to the conditions established for a record to be included in the statistical analysis: a calf weaned normally (raised by the cow and weaned at an age of not less than 5 and not more than 12 months, with a correct code for herd (two herds), sex (male, female) and fasting (seven 6-hour intervals of fasting before weighing), born during months 5 through 9 (9 and 10 combined), of years 1976 to 1987 except 1977,81,83 (when weaning was impossible because of severe floods), classified according to three generations (progeny of foundation cows and two further generations) and out of a cow 3 to 13+ years old.

The data sets for the analysis of Herd A and Herd B included 8160 and 5654 weaning weights, respectively. Both sets were analyzed separately by least squares procedures (Harvey 1990) according to the following model:

Y_ijklmno = a + g_i + s_j + c_k + h_l + d_m + f_n + (ch)_kl + (sc)_jk + (gs)_ij + bA_ijklmno + e_ijklmno

where

Y_ijklmno is the weaning weight of calf "o" belonging to generation "g_i" and sex class "s_j", born in year "c_k" and month "h_l", out of a cow of age class "d_m", with a fasting code "f_n" and with an age at weaning "A".
a= population mean (E_ijklmno = 0).
g_i =effect of generation "i"( i = 1, 2, 3)
s_j= effect of sex "j" (j = 1,2)
c_k = effect of year "k" (k = 1,2…9)
h_l = effect of month "l" (l = 1,2…5)
d_m= effect of age of dam class "m" (m = 1,2…11)
f_n = effect of fasting class "n" (n = 1,2…7)
(ch)_kl, (sc)_jk, (gs)_ij = effect of the respective interactions
b = linear regression of weight on age
A_ijklmno = age of calf at weaning
e_ijklmno = residual (with the usual assumptions).

For the correction of weaning weight to 205 days for purpose of comparisons, mean unadjusted birth weight for Herd A and Herd B was evaluated by a sample taken in several years as 28 and 29 kg respectively.

Results and discussion

Least squares analysis of variance (Table 1) showed a statistical highly significant (P<0.01) effect of all main sources of variance as well as of the covariable age in both herds except the effect of generation which was non-significant (P>0.5) in Herd B. The interaction year x month of birth was significant (P<0.01) in both herds, while the sex x year effect was important (P<0.01) in Herd A but not in Herd B (P>0.05). Generation x sex was an important (P<0.05) effect in Herd A but did not affect the variation of weaning weight in Herd B (P>0.05). These results are, in general, similar to those reported by Bauer et al (1997) for 19887 weaning weights of Criollo and different stages of upgrading this breed to 15/16 Zebu, at the same ranch.

Unadjusted and adjusted means for weaning weight in Herd A were 177.4 ±0.3 and 175.1 ±0.7 kg respectively at an age of 248±0.3 days and in Herd B 174.5 ±0.4 and 174.0 ±0.8 kg respectivly at an age of 250±0.3 days (Table 2).

Using 28 and 29 kg as birth weight, mean adjusted 205-day weight was estimated to be 149.6 kg in Herd A and 147.9 kg in Herd B, giving calves out of Zebu x Criollo dams and sires a 1.7 kg advantage of no economic importance over calves out of Charolais x Zebu x Criollo cows and sires over all generations. Both means are greater or similar to three averages for 205-day weights for large data sets from the same ranch of Criollo Yacumeño (136 kg; Bauer et al 1992) covering the years 1968 to 1982, Zebu elite (146 kg; Galdo et al 1992) of the same time period, and different stages of upgrading Criollo to Zebu (1973 to 1983; 144 kg; Bauer et al 1997). The 205-day weights found in the present evaluation also compare well to the 151 kg (Arango et al 1999), 147 kg (Plasse et al (1999) and 144 kg (Gómez et al 2004) obtained in Bos indicus herds on floodable savanna in Venezuela, but are lower than the 162 kg mean 205-day weight found by Plasse et al (2002b) in a Brahman herd on floodable savanna in the same country, but with better soil quality. They are also lower than the mean 205-day weights reported in two literature reviews from tropical Latin America by Plasse (1978) and Arango and Plasse (1994) which were 161 and 158 kg but derived mainly from ecologically more favourable areas when compared to floodable savannas.

In the F₁ Zebu x Criollo herd (Herd A) generation had a highly significant effect on the variation of weaning weights. Adjusted weight was at maximum in the calves produced in the first generation (G₂), that is by interbreeding F₁ cows and bulls (Table 2). It decreased 10.5 kg (6%) in the next generation (G₃). This tendency would be according to theory, since F₁ cows have the highest degree of heterozygosity (theoretically 100%) and should exhibit the maximum degree of heterosis for maternal ability. Besides that, their calves should maintain approximate 50 % of the heterosis for growth rate of F₁ animals. Weaning weight of 3/4 Zebu calves out of F₁ Zebu x Criollo cows at this ranch and in Turipaná, Colombia, had a mean advantage of 5% over Zebu (Plasse 1983). The offspring of the second generation of interbred cows (G₃ calves) would be affected by a decrease of heterosis percentage for maternal ability of their dams of 50%. In the Charolais x Zebu x Criollo herd (Herd B) generation was a non-significant effect. Theoretically, one would expect less heterosis for mothering ability in generation-one cows of this herd when compared to Herd A, because of the considerable frequency of combination of Charolais and Criollo genes. However, no explanation can be given for the fact that weaning weight was not statistically different among these three generations. Since no direct control group was maintained, the only real conclusion can be that in generations 2, 3 and 4 Herd A showed a 4.5%, -2.5% and 0% deviation, respectively, from Herd B. For practical reasons, this means that their weaning weights compared within generations were different only for G₂, the calves of the foundation cows.

The performance of composite G₃ and G₄ calves with 3729 and 2727 weaning weights for Herd A and Herd B, respectively, is the best estimate for production in advanced generation of these populations, since no further genetic change except that produced by selection is theoretically to be expected. Since no control Zebu herd was maintained along with the crossbreds, the only way to compare their performance with an alternative population would be with the calves of the selected Zebu herd kept on the same ranch between 1967 and 1982 and whose 4363 weaning weights were published by Galdo et al (1992). Since differences between generations were not significant in that herd, the age corrected adjusted mean of 0.683 kg weaning weight for day of age (derived from Table 2, Galdo et al 1992) was used for this purpose. Equivalent values of Herd A and Herd B for the mean of G₃ and G₄ (derived from Table 2) were 0.695 and 0.700 kg respectively. This gives Herd A and Herd B composite calves a 1.8 and 2.5% advantage for weaning weight over contemporary Zebu calves in the same location. This is approximate, but is the only possible estimate of compared weaning weights and confers the composite calves of both herds a small advantage of no economic significance. This is much less than the 15% mean advantage obtained for G₃ and G₄ of MARC I, II and III Bos taurus composites over the respective pure breeds as reported by Gregory et al. (1991) in Nebraska, USA. These authors showed that loss of heterosis over generations was according to expectations from loss of heterozygosity. To our knowledge, no analyzed data on several generations of Bos taurus x Bos indicus composites have been published from Latin America.

The sex difference for Herd A and Herd B was 12 and 8%, respectively, in favour of males. Although these values are similar as those reviewed from the literature (Plasse 1978; Arango and Plasse 1994), the important difference between herds cannot be explained. Year constants oscillated strongly and there was more yearly variation in Herd B than in Herd A (Tables 1 and 2). It is possible that Charolais genes provided the calves with more growth potential, which they could manifest phenotypically in favourable years (good grass and sanitary conditions), but which prevented adaptability to unfavourable years. The same might be the reason for greater variability among months of birth in Herd B than in A. Calves born in May and June, the first part of the dry season, reached the highest weaning weights because during this time floodable savannas supplied optimum nutritional level for them and their dams, while those born during August and September had the lowest weights, since they were born in the driest months and were still young when heavy rains and floods occurred. Age of cow effects were very similar in both herds being highly negative for first calving cows, because they entered the breeding herd with low weights (mean 270 kg). There were small differences between age groups of 5 to 11+ years. Month of birth and age of cow effects behaved similarly to those found for the Criollo Yacumeño herd (Bauer et al 1992) and the Zebu elite herd (Galdo et al 1992) at the same ranch.

The highly significant effect (P<0.01) of time of fasting (Table 1) was of practical importance and required data adjustment. The pattern was very similar in both herds (Table 2): there were no differences between calves fasted 6 or 12 hours, but after that, weight loss was evident and accentuated for calves fasted 31 to 36 and 37 to 42 hours. In Herd A and Herd B calves fasted up to 6 hours weighed 15 and 13 kg (9 and 8%), respectively, more than those fasted 37 to 42 hours.

Conclusions

• Composite Bos taurus x Bos indicus populations would, theoretically, be the only continuous crossbreeding system functionally feasible under tropical Latin American conditions, except the specific case of rotation between Zebu and Criollo as published by Plasse et al. (2002a) from a study realized at another ranch in Beni, Bolivia. However, in advanced generations the composites need to generate a production level which can compete with the results of a modern selection programme in zebu cattle.

• Annual genetic trend for 18-months weight in Venezuela has been reported to be 1 kg in a single Brahman herd ( Plasse et al 2004) and 1.4 kg in a cooperative breeding programme with Brahman cattle including strategic use of artificial insemination and breeding value evaluation (Seprocebu 2005). In the present study no Zebu control group was available, but a comparison with published data from a Zebu herd at the same ranch indicated that Herd A and Herd B had a 1.8 and 2.5% advantage in age-adjusted weaning weight, which we do not consider to be economically important. In Herd A mean weaning weight decreased significantly over generations, while in Herd B no significant change was found. The final judgment about these two composites under the prevailing conditions needs to await the discussion of cow production in the accompanying paper (Plasse et al 2005).

Acknowledgments

The authors thank Computer Annalist Mayanin Dagger for assistance in the preparation of data for the analyses. The authors most gratefully acknowledge the contribution of Professor Lucia Vaccaro in the preparation of the manuscript and her valuable suggestions; they also thank Professor Jesus Arango for reading the manuscript and his valuable comments. The analyses of the data were supported by the Consejo de Desarrollo Científico y Humanístico (UCV) through Ayuda Institucional "A" N° 11.10-5027-2002, which is gratefully acknowledged.

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