Reproductive performance of three brazilian beef breeds

* Centro de Energia Nuclear na Agricultura, Universidade de Såo Paulo, Piracicaiba, Brazil;
** Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, N1G 2W1 Canada;
*** Faculdade de Medicina Veterinária e Zootecnia, Universidade de Såo Paulo, Såo Paulo, Brazil.

The interval from parturition to initiation of cyclic ovarian activity was determined by sequential monitoring of milk progesterone in suckled Gir (n=36), Nellore (n=37) and Caracu (n=37) cows. The animals were maintained throughout the year on grass pastures in a semi-arid region without additional energy or protein supplements. Calvings were concentrated in December and January during the rainy season and bulls were introduced the following March through June for rebreeding. Significantly more Nellore cows (68%) commenced cyclic activity before 3 months postpartum and the response in multiparous (47%) was better than in primiparous (28%) females (P<.05). Evaluation of the pre- and post- sampling intercalving periods for all cows indicated very few achieved annual calvings. The mean intervals were 640 days for Gir, 601 days for Caracu and 468 days for Nellore (P<.05). Thus, calving in alternate years would be typical of the Gir and Caracu breeds but many Nellore cows could produce two calves in three years. Gir cows lost substantial weight and Caracu cows lost a moderate amount during lactation while Nellore cows essentially maintained body weight during this period. Nellore calves gained less weight than those nursing Caracu cows (P<.05) but growth was not significantly different from calves nursing Gir cows. The Nellore, a Bos indicus breed, demonstrated superior reproductive performance when compared with the Gir (Bos indicus) or Caracu (Bos taurus) breeds.

KEY WORDS: Zebu, Gir, Caracu, Nellore, Bos indicus, Bos taurus, reproduction, Brazil, tropics, growth

The continued production of any livestock commodity depends on reproduction, so reproductive efficiency is a major factor in both biological and economic efficiency. Data from Brazilian crossbreeding and new breed development projects were summarized to calculate relative breed differences (Barbosa and Duarte 1989) but sufficient information was only available for predictions on calf weights and carcass traits. These authors pointed out that more factual knowledge is needed on reproductive performance before the various available breeds could be evaluated accurately for total merit. Also, there are suggestions that Bos indicus or Zebu type cattle have inferior reproductive performance compared with Bos taurus breeds. However, most of the basis for criticism comes from results with a single breed, the Brahman, or obtained in uncontrolled situations under less than ideal environmental conditions. To determine whether a general condemnation was appropriate and to provide additional information that might be of use in future planning, the intervals from calving to initiation of ovarian cycles and days open were compared between two Bos indicus breeds (Nellore and Gir) and one Bos taurus breed (Caracu) maintained under identical conditions in a semi-arid, tropical environment.

All experimental animals were purebred beef cows or heifers from the Caracu (Bos taurus) or Gir and Nellore (Bos indicus) breeds maintained at the "Centro Intraunidade de Zootecnia e Indústrias Pecuárias Fernando Costa", Pirassununga, Såo Paulo State, Brazil. This is a tropical area having distinct wet and dry seasons with rainfall concentrated from November to May or June. The station husbandry follows traditional management practices for regional beef herds, with cows maintained entirely on pastures. Breedings occur between the middle to near the end of one rainy season so successfully remated females should calve early in the next period of increased rainfall.

Experimental animals were grazed as a single herd on Panicum maximum grass pastures with a regular rotation and, except for occasional provision of a mineral mixture, no supplementary feed was available. The calves remained continuously with their dams until weaning at the end of the rebreeding period when calves would be 6-7 months of age. Bulls were introduced from March through June each year with an approximate ratio of one male per 15 females. Cows and their calves were weighed at parturition and again at the end of the breeding period so weight changes could be calculated.

Data on intercalving intervals were tabulated from herd records over a 48 months period including all parturitions occurring from mid 1985 until mid 1989. More intensive observations were confined to groups of females that calved between December 24, 1986 to January 30, 1987 (n = 36) and between October 10, 1987 to January 31, 1988 (n = 74), with 71 of the 74 parturitions in the later group occurring during December or January. In addition to results on ovarian activity and intercalving intervals collected after these parturitions, the preceding intercalving intervals were included for all multiparous cows. The actual number of first, second and later parity animals that could have provided intercalving intervals for the individual breeds were respectively: Caracu, 15, 18 and 28; Gir, 13, 22 and 29; Nellore, 16, 7 and 36. Milk samples were collected twice weekly from the two calving groups commencing about two weeks postpartum and continuing for approximately 120 days. The concentration of progesterone was determined in milk samples using solid phase RIA kits supplied by the FAO/IAEA Animal Production and Health Section from the IAEA Applications Laboratory, Seibersdorf, Austria. The intra and inter- assay coefficients of variability were 7.1% and 9.16%. Sequential milk progesterone values were plotted to establish individual profiles for each cow. These were evaluated as previously described (King et al 1976) to determine when ovarian activity commenced.

Discrete data were analyzed by simple or Logit Chi-square and continuous data were evaluated by least squares analysis (SAS 1985) with square root transformation.

Analysis of the continuous data showed that days from parturition to first ovulation, as determined by sequential monitoring of plasma progesterone concentrations, were significantly (P<.05) longer for Gir cows as compared with the other two breeds. The intercalving interval for Nellore cows was significantly (P<.05) shorter than for either of the other breeds (Table 1). Suckled Bos taurus, Hereford and crossbred beef cows maintained in a temperate climate, fed adequate amounts of a balanced ration and calving in the spring season initiated ovarian activity at 59.1 ± 20.3 days postpartum (King and MacLeod 1984). Thus, the Nellore females were able to initiate post partum ovarian activity almost as quickly as suckled cows in a temperate environment while the other two breeds were somewhat slower.

Table 1: Days From Parturition to First Ovulation and Inter-Calving Interval for Three Brazilian Beef Breeds.

Breed	Caracu	Gir	Nellore

Days to ovulation
No. of animals	18	19	34
Average days	81.2	90.7	70.2
Range	35-152	30-156	10-157
Root mean + sem*	8.8±0.4a	9.5±0.4b	8.1±0.3a
Inter-calving interval
No. of animals	35	42	48
Average days	601	640	468
Range	346-1147	338-1521	322-1526
Root mean + sem*	24.1±0.7c	24.5±0.6a	21.7±0.6b

* Square root transformation used in least squares analysis.
Row values with same superscript are not significantly different P<0.05.

The continuous data was only available for animals that started cycling before day 120, so a comparison of proportional responses for animals ovulating by day 90 was also made. The actual number of animals that commenced cyclic ovarian activity by day 90 and total number sampled for progesterone determination in the various breeds were: Caracu, 12 of 37; Gir, 9 of 36; and Nellore, 25 of 37. The responses were further subdivided into primiparous and multiparous groups within each breed for analysis by Logit Chi-square. This indicated differences were significant (P<.05) for both breed and parity, but not for the interaction. More Nellore cows (68%) commenced cyclic ovarian activity by 3 months post partum and at least had opportunity for conception in time to maintain annual calving, but only 25% of Gir and 32% of Caracu cows had ovulated by this time. The comparison of response in first calf heifers and later parity cows showed that 9 out of 32 (28%) primiparous and 37 out of 78 (47%) multiparous females ovulated one or more times up to day 90 (P<.05). Thus, both breed and parity influenced the return of cycle ovarian activity after calving. Only two Caracu, two Gir and eight Nellore intercalving intervals were less than 365 days (X² = 1.46, P>0.01). Therefore, none of the breeds were very good at maintaining annual calvings. However, under the conventional management system for the region, cows that calved during traditional calving season, between November and late January, could be re-bred between the following mid March to late June. Thus, animals calving in one year and becoming pregnant during their next breeding opportunity could have intervals as long as 450 days. Nine of 61 Caracu, 13 of 64 Gir and 33 of 59 Nellore had intercalving intervals less than 450 days (X² = 29.17, P<0.01), indicating that significantly more Nellore females conceived during the mating period immediately after calving. Alternate year calving is probably a reasonable expectation in the semi-arid tropics unless supplemental feed is provided during the dry season and any other times when metabolic demands are increased. Many cows in the Caracu and Gir breeds appeared to follow this pattern. In contrast, the mean interval for Nellores indicated that a substantial proportion of individuals with this genotype might be capable of producing two calves in three years.

The parturition to weaning body weight changes for cows and their calves are shown in Table 2. Gir cows lost considerable weight and Caracu a moderate amount while Nellore were almost able to maintain weight during lactation. Since the mean weights were reduced in all three breeds, females had to draw on body reserves to sustain lactation even though they were grazing on improved pastures during the active growing season. This metabolic demand precluded additional reproductive functions in many of the Caracu and Gir females but most of the Nellore could initiate oestrus cycles while lactating. The former two breeds demonstrated prolonged periods of acyclicity, apparently electing to devote a major portion of resources towards survival of the suckling calf at the expense of reconception. This is certainly true for the Caracu breed whose calves gained significantly more weight than those nursing Gir or Nellore cows. The Nellore cows essentially maintained body weight while lactating a sufficient amount for reasonable calf growth and commenced ovulating in time to at least have some chance of annual calvings. The substantial weight loss and prolonged acyclicity demonstrated by Gir females during lactation was not compensated for by high offspring growth since these calves gained no more weight than those nursing Nellore dams.

Table 2: Mean Values for Weight Change (kg) of Cows and Calves Between Parturition and Weaning for Three Brazilian Beef Breeds*

Breed	Cows	Calves

Caracu	-14.0±3.5a (36)	84.1±2.8a (27)
Gir	-29.0±3.5b (36)	76.1±2.5b (36)
Nellore	-3.5±3.6c (37)	74.7±2.5b (34)

* Figures in parenthesis are number of observations.
Column values with same superscript are not significantly different, P<0.05.

As stated in the introduction, aspersions are sometimes cast at all Bos indicus or Zebu animals based on results obtained with a single breed, the Brahman. This is analogous to proposing that the Hereford typifies phenotype for all Bos taurus animals. In actual fact, Bos taurus phenotypes range from miniature Dexters to massive Chianinas and Hereford color, size, conformation or physiological mechanisms are quite dissimilar to many other breeds in this species. Undoubtedly, some Bos indicus breeds have less efficient reproductive performance than some Bos taurus breeds but the reverse may also be true. Some Zebus, like the Nellore in Brazil or the Kedah-Kelantan in Malaysia (Tan et al 1986), have adapted to local environments and demonstrate good reproductive performance under less than ideal conditions. Perhaps the most important aspect of the results presented is that not all Zebu breeds should be painted with the Brahman brush.

The contributions of staff at "Centro Intraunidade de Zootecnia e Indústrias Pecuárias Fernando Costa" in providing experimental animals, facilities and technical assistance; the FAO/IAEA Joint Section of Animal Production and Health for provision of operating funds and hormone assay kits (Research Contracts 4524/RB and 3784/R1/RB) and the Ontario Ministry of Agriculture and Food for data analysis facilities are gratefully acknowledged.

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King G J and MacLeod G K 1984. Reproductive function in beef cows calving in the spring or fall. Animal Reproduction Science 6: 255-266.

Tans H S, Kassim H and Mak T K 1986. Reproductive performance of indigenous cattle in Malaysia. In: Nuclear and related techniques in animal production and health. IAEA Proceedings Series (STI/PUB/717) 189-203.