| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ANIMAL GENETICS |
* Department of Animal Production, College of Agriculture Luiz de Queiroz, University of Sao Paulo, Piracicaba, Sao Paulo, Brazil; and
Southeast-Cattle Research Center, Embrapa, Sao Carlos, Sao Paulo, Brazil
 |
Abstract |
|---|
 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
Charolais + 
Zebu), whereas calves from NL cows were sired by Nellore bulls. Cows were individually fed a pelleted diet with 50% hay (alfalfa and coastcross) and 50% concentrate from calving to weaning (20 to 180 d post-partum). Estimated diet ME content was 2.24 Mcal/kg of DM. Individual cow DMI was adjusted every 14 d to keep shrunk BW and BCS constant. Shrunk BW and BCS were 430 ± 12 kg and 4.7 ± 0.09 for NL, 449 ± 10 kg and 4.8 ± 0.09 for CN, 496 ± 10 kg and 5.0 ± 0.09 for AN, and 507 ± 12 kg and 5.1 ± 0.09 for SN. At 40 d calves were allowed ad libitum access to the same diet. Milk yield was recorded using a weigh-suckle-weigh technique. Increasing B. taurus percentage had a linear effect (P < 0.01) on ME intake (MEI) of cow/calf pairs: 21.9 ± 0.38 for Nellore, 23.6 ± 0.35 for 31.5% B. taurus (CN), and 25.6 ± 0.27 Mcal/d for 50% B. taurus (AN and SN). Bos taurus percentage was also positively associated with milk production. Nellore calves had lower (P < 0.05) weaning weight (kg) than crossbreds: 167 ± 12 vs. 206 ± 10 for 
Canchim 
Nellore (C), 220 ± 11 for 
Canchim Angus Nellore (A) and 228 ± 11 for Canchim Simmental Nellore (S). Calf body composition was estimated at weaning using the 9-10-11th-rib section. Retained energy (Mcal) was greater (P < 0.05) in A (384 ± 19.9) than in Nellore (298 ± 21.6) and C calves (312 ± 19.8), and was intermediate in S calves (333 ± 21.6). Cow/calf energetic efficiency (kcal deposited/Mcal of MEI by the pair) was greater (P < 0.05) for AN (103 ± 5.3) than NL (84.9 ± 5.9), CN (83 ± 5.3), and SN pairs (83.5 ± 6.1). Difference (P < 0.05) between Continental and British crosses was shown in linear contrasts; SN pairs had greater MEI and lower retained energy than AN. Increasing the B. taurus percentage increased inputs as well as outputs. However, a relatively greater increase in outputs resulted in significantly greater preweaning efficiency. Purebred Nellore had lower ME requirements; however, in an environment without nutritional constraints, crossbreeding improved preweaning biological efficiency.
Key Words: biological efficiency • body composition • crossbreeding • milk production • weaning weight
|
INTRODUCTION |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
). Recent work with growing animals has shown that profit can be improved to a greater extent through increases in feed efficiency rather than increases in outputs (Arthur et al., 2001). Cow/calf efficiency can be measured by gross efficiency, defined as calf weaning weight divided by total feed intake, as well as energetic efficiency, defined as calf energy retained/MEI by the cow/calf.
In Brazil, purebred Nellore and its crosses represent around 75% of the total national herd, thus over 150 million animals, carry mostly Nellore germplasm. Crossbreeding programs have introduced different breed types with greater productive potential. Bos taurus x Bos indicus crosses benefit from the effects of heterosis and complementarity. Unfortunately, these effects have the potential to increase energy requirements (Jenkins and Ferrell, 1983; Ferrell and Jenkins, 1984) and weight at puberty, which could result in lower reproduction rates in nutritionally restricted environments (Dickerson et al., 1974).
If compared with input/output ratio, body size itself has little impact on determining economic efficiency of beef production systems (Dickerson, 1978). Tess and Davis (2002) suggested that cows of lower mature size could be mated to terminal sires with greater growth potential. However, knowledge of feed requirements for different breeds is vital to match maternal breed types to the environment. Studies reporting feed intake, nutrient requirements, and efficiency of cows of tropically adapted breeds are scarce.
This study was designed to determine the ME requirements of lactating cows and the efficiency of cow/calf pairs to evaluate if energy requirements are parallel to milk yield, mature weight, and B. taurus percentage by comparisons between purebred Nellore and its crosses with Continental and British B. taurus breeds.
|
MATERIALS AND METHODS |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
All procedures with animals were conducted according to the University of Sao Paulo ethical standards established by the College of Agriculture Research Commission.
This study was conduced at Southeast Cattle Research Center (Embrapa), Sao Carlos, Sao Paulo, Brazil, from March to December of 2002. Beginning in 1997, 300 Nellore cows were assigned by age, BW, BCS, and origin to 5 homogeneous groups (60 cows each). Cows were then bred by natural service to Nellore or Canchim ( Charolais + Zebu) bulls or were artificially inseminated to Simmental or Aberdeen Angus bulls. Two B. taurus bulls of each breed were chosen, given market availability, and each had high and positive EPD for yearling weight (30 kg for Angus and 35 kg for Simmental). The EPD values did not influence the choice of bulls. The first calf crop was born in 1998, and part of this generation was used in the study.
At the beginning of the experiment, Nellore and cross-bred females were 47 ± 1.5 mo of age and on their second or third calf. Ten cows for each breed type were identified for use in the study. The Canchim x Nellore (CN), Angus x Nellore (AN), and Simmental x Nellore (SN) cows were mated to Canchim bulls, whereas the Nellore (NL) females were bred to Nellore bulls.
Before the experiment, the 40 pregnant cows were maintained on pasture and received a mineral salt supplement. Cow’s BCS ranged from 5 to 6 (1 to 9 scale) from calving to the beginning of the study. The 40 cow/calf pairs were randomly assigned to 1 of 10 blocks by calving date, with 1 pair of each breed type. The trial was conducted from 20 to 180 d postpartum. There were 5 male and 5 female groups of calves in the Canchim Nellore (C) and the Canchim Simmental Nellore (S), 6 males and 4 females in the Nellore group, and 4 males and 6 females in the Canchim Angus Nellore (A) group. One Nellore (female) and 1 S (male) calf died before weaning. For these animals, the weaning weight, the last 50 d of feed intake, and the slaughter data were not collected. All male calves were left intact.
Cows were distributed in individual pens with their respective calves and fed a pelleted diet (Table 1) containing 50% hay (15% alfalfa and 35% coastcross) and 50% concentrate, on a DM basis. Crude protein and ME content were 16.1%, and 2.24 Mcal/kg of DM, respectively. The ME content of the diet was estimated according to the equation of Weiss et al. (1992), considering 0.75 as the rate of degradation of the potentially digestible NDF. At 40 d of age, calves were allowed ad libitum access to the same diet. Cow and calf feeders were separated physically so that cows had no access to the calves’ feeders and vice versa and so that individual cow and calf intakes could be recorded. Animals were fed twice daily at 0800 and 1600. Orts were collected, weighed, sampled for DM analysis and discarded daily. Cows and calves were weighed at 14-d intervals, during which BCS of cows were also evaluated by 2 trained evaluators.
|
). Before each sampling, calves were removed for 16 h. Calves were then weighed, allowed suckling under constant observation, and then reweighed. This was repeated after the pairs were separated for another 8 h. The daily milk yield was determined by adding the 16- and 8-h weight changes. At 80 and 150 d postpartum, calves were removed for the same 16- and 8-h intervals, and each cow was milked in the same sequence. Samples of each milking were combined for analysis. To aid in milking, 2 mL of oxytocin (Ocitocina Forte U.C.B., Jaboticabal, Brazil) per cow per milking was administered. Total milk yield at 180 d of lactation for each cow was calculated as Y180 = (Y1 x I1) + 
{[(Yi + Yi – 1)/2] x Ii} + (Yn x In), where Y1 is the milk yield at the first milk production control; I1 is the interval between calving and the first control; Yi indicates the milk yields at the intermediate controls (from 2 to 4); Ii indicates the intervals between 2 consecutive controls; Yn is the milk yield at the last milk production control; and In is the interval between the last control and weaning [ABCBRH (Brazilian Cattlemen Holstein Association), 1986]. Fat-corrected milk production was calculated according to the equation of Gaines (1928). Total milk solids were determined and milk samples were analyzed for fat, protein, and lactose by infrared spectrophotometry using Bentley 2000 equipment (Bentley Instruments Inc., Chaska, MN).
Secreted milk energy was estimated using values of 9.29, 5.47, and 3.95 Mcal/kg for fat, protein, and lactose, respectively (NRC, 2001). Milk MEI for the calves was estimated using the ratio, 1:0.93, between milk GE (milk energy secreted) and ME (NRC, 2001).
Energetic Requirements and Efficiency of Cows
Animals were adapted to pens, and feed was initially offered based on estimated NE requirements for maintenance and lactation, according to the NRC (1984 and 1996). The adjustment coefficients for milk production of each breed type were 100 for SN, 97 for AN, 96 for CN, and 94 for NL. Milk yield at peak lactation was assumed as 11, 9, 8, and 6 kg/d, for SN, AN, CN, and NL, respectively (NRC, 1996). The DM intake of each individual cow was adjusted at 14-d intervals to keep shrunk BW (SBW) and BCS constant. Cows gaining BW received 5 to 15% less feed than offered in the previous 2-wk period, and those losing weight received 5 to 15% more.
For individual energy balance calculations, the retained or lost energy due to BW changes were addressed using a system reported by Fox et al. (1992). An average value of 5.6 Mcal/kg would be appropriate when BCS is 5 in a scale of 1 to 9. Cows with BCS lower than 5 would have less energy in 1 kg of BW gain. The average BCS of cows in this experiment was 4 to 5, therefore a value of 5.2 Mcal/kg of lost or gained empty BW (EBW) was used. Cow EBW was considered 85.54% of BW (D. P. D. Lanna, University of Sao Paulo, Piracicaba, Sao Paulo, Brazil, personal communication). The adopted value for the efficiency with which mobilized NE from body tissues is used to secrete milk was 0.82 (Van Soest, 1994). Total milk energy secreted minus the NE for lactation from mobilized tissue corresponds to the energy used for milk synthesis. To calculate ME requirement for milk synthesis, the efficiency value of 0.62 was used (Van Soest, 1994). For cows that stored body reserves, an energetic efficiency of 0.75 was considered (Van Soest, 1994).
Experimental Slaughter
Calves were slaughtered at weaning (188 ± 17 d of age). Hot carcass weight and liver, kidneys, heart, and kidney-pelvic fat weights were recorded. After a 24-h chill, right and left sides of the carcass were weighed (chilled carcass weight), and the left side was separated. Carcass data included length, depth, LM area, and 12th-rib fat thickness. The 9-10-11th-rib section was removed according to Hankins and Howe (1946) for body composition estimation. Body composition at birth was considered as 77.5% water, 4.0% fat, 14.7% protein, and 3.5% ash for all groups (Haigh et al., 1920). In view of the much larger BW gained relative to birth weight, any differences in composition at birth would have minimal consequence for the estimates of the composition of gain.
The 9-10-11th-rib sample was ground through a homogenizer (Hermann P-33A-3-789, 15 HP) and samples freeze-dried. The frozen sample was ground, homogenized, and a subsample was taken for chemical composition analysis. Protein was determined using the standard macro-Kjeldahl method (AOAC, 1990), and fat was analyzed using the chloroform-refluxing Soxhlet apparatus.
Calves’ EBW was estimated from HCW based on the equation developed by Henrique et al. (2003). Empty body chemical composition was estimated from linear regressions of percent water and fat in the 9-10-11th-rib. Equations used for Nellore calves were the same developed for Nellore bulls by Lanna et al. (1995), and equations used for the crossbred calves were developed by Henrique et al. (2003) for B. taurus x B. indicus crosses. The original Hankins and Howe (1946) methodology was modified, so that the entire rib sections (bones and soft tissue) were ground. The composition of the entire 9-10-11th-rib was used. Protein and ash in the empty body were calculated from the estimated fat and water using the 80:20 ratio of protein and ash in the fat-free DM (Reid et al., 1955; Boin et al., 1994). The energy concentration used for protein and fat was 5.497 and 9.390 Mcal/kg of EBW, respectively (Ferrell et al., 1976).
Statistical Analyses
Analyses of variance were performed with the GLM procedure (SAS Inst. Inc., Cary, NC), using models with fixed effects of breed type, block, and sex of calf. Cow BCS were included as a covariate to evaluate energy requirements and energetic efficiency of cows and cow/calf pairs. Because multiple sires were used, a sire effect could not be included in the model. Interaction of breed type, calf sex, and parity were evaluated, and those not significant were removed from the model. Tukey’s test was used to compare breed-type means. The effect of an increasing percentage of B. taurus (0, 31.5, and 50%) was evaluated by linear and quadratic contrasts using PROC GLM. The linear contrast was used to estimate the change in energy requirements of cows and the efficiency of cow/calf pairs by comparisons between NL vs. crossbred, CN vs. F1, and AN vs. SN. Cow BW at the beginning of the trial and at weaning were analyzed using the paired t-test procedure (SAS Inst. Inc.) to evaluate the difference between initial and final BW. Selected results of the ANOVA are presented in Table 2.
|
|
RESULTS AND DISCUSSION |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
There were no differences between initial and final SBW of cows. However, the individual numerical changes observed during the course of the trial were considered to calculate tissue mobilization or deposition and energy balance. These calculations were required to estimate maintenance energy requirements.
Nellore and CN cows had lower BW (P < 0.05) than AN and SN. The heavier BW of SN crosses were expected, but it was not expected that Angus and Simmental crossbred cows had similar BW. This may be explained by the high EPD for yearling BW of the Angus sires used in the study.
Milk Yield, Milk Composition, and Milk Energy Secretion
The increase in B. taurus percentage had a linear effect on milk production (P < 0.01), 22% greater for 31.5% B. taurus blood, and 37% greater for 50% B. taurus (AN and SN) compared with purebred Nellore cows. These results are consistent with previous data indicating that Zebu cattle have lower milk production potential (Alencar et al., 1993; Cruz et al., 1997). Simmental crossbred cows had greater total milk production (P < 0.05) than NL and CN, but did not differ from AN cows. Total milk yield corrected for 4% fat was also greater (P < 0.05) for SN than NL cows, with AN and CN groups showing intermediate values. Average daily milk production (kg/d) was 6.6 ± 0.50 for SN, 5.4 ± 0.48 for AN, 4.7 ± 0.48 for CN, and 3.7 ± 0.50 for NL cows. It should be noted that NL cows from this experiment had straightbred Nellore calves, whereas the crossbred cows had crossbred calves with greater growth potential. However, lower milk yield by NL cows compared with crossbred had previously been described for Nellore cows suckled by crossbred calves. Alencar et al. (1993) and Cruz et al. (1997) documented greater daily milk production for Canchim over Nellore cows when these were suckled by Canchim x Nellore calves (5.87 vs. 3.78 kg/d). The observed differences for milk production potential for NL cows may indicate lower energy requirements during lactation, which can be an advantage under environments with limited feed resources.
Although NL cows had lower milk yield, milk fat content was greater (P < 0.05) than AN and SN. Milk fat concentration for CN was intermediate. These results agree with previous comparisons by Cruz et al. (1997) in which Canchim cows produced more milk of lower fat content than Nellore (1,269 kg and 4.74% vs. 883 kg and 5.53% for a 238-d lactation). Milk protein concentration was also greater (P < 0.05) for NL cows than AN and SN, whereas CN had intermediate values. Data reported for B. taurus crosses under temperate environments are similar to those observed for the AN and SN crosses (Chenette and Frahm, 1981; Beal et al., 1990; Marston et al., 1992).
Cow Energy Requirements
The effect of B. taurus percentage was evaluated (Table 3). When the contrast was significant, a linear effect was present. It demonstrates that the mean values have a positive correlation with B. taurus percentage.
|
). These results agree with Ferrell and Jenkins (1984), Montaño-Bermudez et al. (1990) and Jenkins et al. (1991) who reported that daily MEI was greater for cows with a heavier mature BW and greater milk production. Daily MEI of NL cows was lower (P < 0.05, Table 5) than the other groups: 205 ± 3.7 kcal·kg of BW–0.75·d–1 for NL, 216 ± 3.5 kcal·kg of BW–0.75·d–1 for CN, 227 ± 3.5 kcal·kg of BW–0.75·d–1 for AN, and 231 ± 3.8 kcal·kg of BW–0.75·d–1 for SN. There is evidence that differences exist among breeds of cattle in efficiency of energy use for maintenance and that these differences are correlated to differences in productive potential of breeds (Archer et al., 1999).
|
|
and Jenkins and Ferrell (1993). Similar results have been verified for other breed types with high milk production potential and large mature BW. Jenkins et al. (1991) compared crossbred cows and demonstrated greater requirements for Brown Swiss (29.1 Mcal/d) compared with Red Poll and Angus x Hereford (26.5 and 26.9 Mcal/d, respectively). Brown Swiss crossbred cows had greater mature BW and greater milk production potential, which can be an advantage when feed cost relative to revenue are low to moderate, but a disadvantage under other pricing scenarios.
Data from this and other experiments (Boin, 1995) are consistent in demonstrating lower MEI and requirements of Zebu breed types. However, Green et al. (1991) found MEI for Brahman x Angus or Hereford (27.7 Mcal/d) to be greater than MEI of Angus x Hereford (24.1 Mcal/d). The reason for this is that the Brahman x Angus/Hereford dams had greater mature BW and greater milk yield than Angus x Hereford dams, demonstrating that comparisons need to take into consideration the crossbreeding scheme and heterosis.
The ME requirement for maintenance (MEm, kcal·kg of BW–0.75·d–1) was calculated using individual estimates for BW and BCS change, MEI, and milk secretion. Values were not different (P > 0.05) between NL and crossbred cows (Table 5
); moreover, increasing B. taurus percentage did not contribute (P > 0.05) to greater maintenance requirements (Table 3, Table 4). Although not statistically significant, NL cow requirements were about 6% lower than requirements of Bos taurus crosses. Crossbred cows had a 50% contribution from Bos indicus genes, and the 6% difference is similar to that suggested by NRC (1996), which considers maintenance energy requirements for British x Zebu crosses 5% lower than those from British breeds.
Crossbred cows (50% B. taurus) were characterized as having the greatest milk production and had a greater proportion of daily MEI used for lactation (Table 4, Table 5). The daily ME requirement for lactation (ME1, kcal·kg of BW–0.75·d–1) was greater (P < 0.10) for 50% B. taurus (75.8 ± 5.3) than for NL cows (59.2 ± 7.4), whereas cows with 31.5% of B. taurus blood (69.1 ± 7.1) were intermediate. A positive linear effect of B. taurus percentage was demonstrated (P < 0.10). In this experiment both the greatest MEI and the greatest milk energy secretion were observed in the same breed type. This is consistent with other data available, which suggest that animals with greater production potential (greater energy requirements) may perform poorly in nutritionally limited environments (Ferrell and Jenkins, 1984, 1985). Thus, these breed types may be less efficient under stressful conditions. When nutrition is improved, animals with high growth and milk production potential (e.g., Simmental crossbred) may be biologically and economically more efficient. Solis et al. (1988) reported breed differences in energy requirements for maintenance among Jersey, Holstein, Brahman, Hereford, and Angus. Mating systems designed to utilize between- and within-breed differences in energy expenditure for maintenance offer an opportunity for improving energy efficiency (Johnson et al., 2003).
Calf Performance, Feed Efficiency, and Body Composition
Nellore calves were lighter (P < 0.05) at birth and at weaning, and had the lowest rates of BW gain compared with crossbred calves (Table 6). Nellore calves consumed less ME (pelleted diet plus milk). Although differences were not significant, the C calves consumed 15% more pelleted diet than the A and S calves, who ingested 7 and 20% more milk, respectively (Table 6). Wyatt et al. (1977) observed the greatest milk intake associated with the lowest forage intake. Results from the crossbred calves in this experiment support this observation. Compared with crossbred animals, Nellore calves had greater BW gain per kilogram of milk intake (P < 0.05, Table 6). Some experiments (Wyatt et al., 1977; Alencar, 1989) have shown that cows with high milk energy secretion have calves with low gain/milk efficiency. Alencar (1989) noted that greater milk production increased the amount of milk necessary to produce a unit of BW gain.
|
). Females had greater fat (P < 0.01) and lower water (P < 0.01) concentrations in the empty body than did males, independent of breed (13.1 ± 0.57 and 62.7 ± 0.54 vs. 10.2 ± 0.60% for fat and 65.5 ± 0.57% for water content). Similar results had been presented by Anrique (1976), with Angus and Holstein calves.
|
A calves had lower (P < 0.05) empty body water content than the other groups and greater (P < 0.05) empty body fat than C and S (Table 8). Despite lower EBW, Nellore had similar chemical fat content. Nellore is typically considered a late maturing breed because puberty is exhibited at older ages. However, when compared at the same BW, Nellore has been shown to have a greater proportion of fat in the empty body than any of the B. taurus crossbreds (Berndt et al., 2001). Nellore cattle have been shown to have the same chemical empty body composition when approximately 100 kg lighter than Simmental x Nellore steers (Berndt et al., 2001).
|
A calves had greater (P < 0.05) empty body energy (426 ± 20.9 Mcal) than C (357 ± 20.8 Mcal) and Nellore (332 ± 22.6 Mcal), S calves were intermediate (385 ± 22.6 Mcal). Retained energy (RE) is the difference between empty body energy at weaning and at birth (Table 8). The RE was greater for the Angus cross-breds, which displayed greater rates of BW gain and EBW fat contents at weaning. Nellore and C calves deposited less (P < 0.05) empty body energy than A, whereas S calves were intermediate. The same efficiency between Nellore and S calves, despite much greater rates of gain of S calves, suggests that the lower maintenance requirements for Nellore were as effective as the dilution of maintenance, which results from the greater rates of gain for the crossbred. The S calves’ MEI was 25% greater than that of Nellore calves (Table 6), whereas they deposited only 11% more energy (Table 8). Different composition of the EBW gains, with more fat over fat-free for Nellore calves, could also have increased energetic efficiency because protein deposition is energetically less efficient than fat deposition. Efficiency of the Cow/Calf Pair
The MEI for the SN cow/calf pairs was greater (P < 0.05) than for the other groups. The relationship between calf BW gain and energy input for cow/calf (grams of BW gain/Mcal of MEI) revealed that AN pairs were more efficient (P < 0.05) than NL. Means of other crosses did not differ (Table 8). The linear contrast (Table 3) shows that the increase in B. taurus percentage had a significant effect on daily MEI of cow/calf pair (P < 0.01, Table 4). The gross efficiency was 18% greater (P < 0.05) for 50% B. taurus cow/calf pairs, and pairs with 31.5% B. taurus were intermediate (Table 4).
The crossbred animals may have benefited from the heterosis for milk production and for increased calf growth (Green et al., 1991). Jenkins et al. (1991) reported that moderate size cows with moderate levels of milk production are biologically most efficient. Cundiff et al. (1983) considered breeds with lower input characteristics as more efficient when the whole production system was evaluated. However, calf growth potential later in life is an important characteristic to model the entire beef production system. The output/input relationship for the whole production system should improve when moderate size cows with low to moderate requirements are mated to sire breeds with greater genetic potential for growth. The selection within breed to improve the efficiency of the production system should be carried out, particularly for breeds that contribute to the cow herd (Archer et al., 1999). In many production systems the feed used for postweaning growth is a relatively small part of the total feed used for beef production (Gregory, 1972). Because cow/calf requirements represent up to 50% of feed costs, cow/calf efficiency may be a reasonable representation of production system efficiency.
Based on an evaluation of cow/calf efficiency (calves BW gain/cows DMI), Herd (1992) reported significant variation and observed that some cows require up to 50% less feed/kg of calf weaned than other cows from the same herd. The variation in biological efficiency of the total production system is associated with maintenance feed costs of breeding cows, and this suggests a possibility for selection of more efficient animals (Bishop, 1992).
Energetic efficiency of the cow and calf was determined by the ratio of RE in the calf and MEI for both cow and calf (kcal of RE/Mcal of MEI). The AN pairs were more efficient (P < 0.05) at converting energy than the other cow/calf pairs (Table 8), consistent with the increase in efficiency demonstrated in the analysis of percentage B. taurus influence. Reasons for this difference in favor of Angus could be explained by the fact that A calves deposited 23% more empty body energy than Nellore calves, which was more than enough to compensate for the greater MEI (7% greater than the NL pair). The linear contrast shows a difference (P < 0.05; Table 3) between Continental and British crosses, because SN pairs presented greater MEI and lower RE than AN pairs. This increased energy deposition was a product of greater gains and greater final chemical fat content.
The greatest energetic efficiency of the Angus cross confirms that pairs in which the calf has a high rate of BW gain and the cow a moderate MEI should be more efficient. Crossbreeding with any B. taurus improved efficiency as measured by calf BW gain/total energy input to cow and calf (15% greater for 31.5% B. taurus and 22% greater for 50% B. taurus) and increased calf energy deposition. The increase in efficiency with increasing B. taurus influence is related to increases in input and output, but a relatively greater increase in the latter. However, high efficiency has been shown in this and other experiments when energy content was not restricted (Ferrell and Jenkins, 1993; Jenkins and Ferrell, 1993).
Crossbreds presented greater daily energy requirements than straight bred pairs (Table 4). Nellore had lower energy requirements, which is an advantage in a nutritionally challenging environment. In the nutritional environment of this experiment, which allowed requirements to be met, crossbred calves had greater rates of energy deposition. This greater output more than compensated for the greater inputs, and thus efficiency was increased when compared with purebred Nellore, considering 100% of reproduction efficiency. The present experiment demonstrated large differences in energy requirements among breed types, which needs to be taken into account before producers choose which breeds of cows and bulls to use in their production systems.
An increase in B. taurus influence resulted in increases in input (requirements) and output (production) variables; however, the greater relative increases in outputs resulted in an increase in efficiency with increasing B. taurus influence. There was high individual variability (between and within-breed types) for biological and energetic efficiency. Given the potential economic implications of this variability, similar to recent residual feed intake studies, a better evaluation of both genetic and environmental components is necessary. The data from these experiments is in agreement with simulation studies of beef production systems.
|
Footnotes |
|---|
2 Corresponding author: dplanna{at}esalq.usp.br
Received for publication July 7, 2006. Accepted for publication May 29, 2007.
|
LITERATURE CITED |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
This article has been cited by other articles:
|
|
 |
|
  L. Calegare, M. M. Alencar, I. U. Packer, P. R. Leme, C. L. Ferrell, and D. P. D. Lanna Preweaning performance and body composition of calves from straightbred Nellore and Bos taurus x Nellore crosses J Anim Sci, May 1, 2009; 87(5): 1814 - 1820. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. Calegare, M. M. Alencar, I. U. Packer, C. L. Ferrell, and D. P. D. Lanna Cow/calf preweaning efficiency of Nellore and Bos taurus x Bos indicus crosses J Anim Sci, February 1, 2009; 87(2): 740 - 747. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
