Geographical location

This study was carried out in Mexicali, Mexico, which is found at 32° 32´00 N, 115° 12’41 W. The region is characterized by a dry desert climate with an average temperature of 34.7 °C (-5 °C winter and 50 °C summer), with an annual rainfall of 37 mm, and a relative humidity above 50 %¹¹.

Animals and design of the study

The study was performed using castrated Holstein calves between the ages of 7 and 8 mo, with an average weight of 238 ± 0.74 kg. Twenty four hours after the cattle arrived to the feedlot they were vaccinated, dewormed and implanted with a product that contained trembolone acetate, estradiol and tilosine. On arrival during spring (April-June) the animals were assigned to one of two groups so that two treatments may be established. Each treatment included five pens. The first treatment included 65 Holstein steers, in this case each animal had a space allowance of 14 m²/per animal (T14), in the second treatment a 16 m²/animal (T16) was allocated to each of 57 Holstein steers. The cattle were fed twice a day using a feeding program that included three different diets given during the fattening and finalization periods. In different proportions the ingredients of all diets were: sudangrass, wheat hay, tallow, dried distillers grains (DDGs) and a premix minerals.

After a 261 fattening period the steers were slaughtered, the average weight of the group was 604 ± 5.67 kg. On the day the steers were slaughter they were transported 36 km by truck to the slaughter house where they were put in waiting pens for 3.5 h, during this time only water was provided. The steers were slaughter in a Federal Inspection Type slaughter house (FIT) following the procedure described in the Mexican Official Norm NOM-033-SAG/ZOO-2014, “Slaughter methods to be used in domestic and wild animal”

Production behavior

The following production result: initial weight, weight after first reimplant, weight after second reimplant, final weight, average daily gain (ADG) and food conversion, were obtained from the company´s records. Each of the animals slaughter weight was obtained in the stunning box.

Carcass and meat evaluation

Carcasses from both treatments were chilled at 2 °C for 24 h and ribbed between the 12th and 13th ribs to collect additional carcass data. A total of 178 carcasses from T14 and 176 carcasses from the T16 were available by the slaughterhouse to be considered for the study of all the variables. The measurements of hot carcass weight (HCW) and cold carcass weight (CCW), dorsal fat , marbling, ribeye area, pH and color of each carcass were taken. Dorsal fat was measured in mm using a metric ruler. The ribeye area was evaluated using a plastic grid method suggested by Iowa State University and the marbling score (scale of slight; small; modest; moderate; slight abundant; moderately abundant), were both evaluated following the methodology described by AMSA¹². The pH was determined using a potenciometer (HANNAH INSTRUMENTS Inc. pH 101), the color values (L*, a*, b*, C*, H*) were measured on the surface of the cut from the Longissimus dorsi muscle between the twelfth and thirteenth intercostal space using a MINOLTA CM-2002 spectrophotometer (Minolta camera, Co., Ltd., Japan) with a specular component included (SCI), a D65 illuminant, and a 10° observer, where L* is the index of luminosity, a* is the red color intensity and b* is the yellow color intensity and C* measure color saturation.

Statistical analysis

Productive data was analyzed using the following statistical linear model: Yij=μ+τi+βj+εij where Yij is the response variable, μ is the true mean effect, τi is the fixed treatment effect, βj is the fixed pen effect and εij is the random residual error iid N (0, σe2). The hypothesis that treatment effects do not differ, was performed by F test statistic in the ANOVA. Differences between treatments were declared when P≤0.05.

Carcass and meat quality data were analyzed as a randomized complete block design with sampling, with pen as the experimental unit and carcass as the observational unit. The statistical linear model was as follows: Yijk=μ+τi+βj+εij+ δijk, where Yijk is the response variable, μ is the true mean effect, τi is the fixed treatment effect, βj is the fixed pen effect, εij is the random residual error iid N (0, σe2) and δijk is the random sampling error iid N (0, σd2). The hypothesis that treatment effects do not differ, was performed using an F test statistic in the ANOVA. Differences between treatments were declared when P≤0.05.

The hypothesis that treatment effects do not differ for proportions within each marbling class was done using a Chi-square test statistic in one frequency table. Differences between treatments were declared when P≤0.05. The analysis was made using the MIXED and FREQ procedures of the SAS 9.4 (TS1M7) statistical package.

Production results

A relevant finding of this study was that steers with a larger pen space had a higher weight during all the fattening period; these results are presented in Table 1 and show that after receiving the first reimplant (day 94 after arrival to the feedlot), the steers from T16 showed an average higher weight when compared to the animals in T14 (P<0.05); this same result was observed after the second reimplant and through all the fattening period (P<0.05); the observed weight difference between the groups was 16 %. Similar results regarding weight differences have been reported by other authors¹³, who found a higher final weight in Hanwoo steers when they were provided with a larger pen space.

Table 2 shows the production results for both groups of steers. It was found that weight gain was higher for the steers in T16, however no difference was found in feed conversion and feed intake. Similarly, to this study Kim et al¹⁴, observed that Holstein steers 20 mo of age that were provided with 16 m²/animal, reached a 750.39 kg final weight and daily weight gain of 1.36 kg. A study in Holstein steers that did not considered the amount of living space per animal as a variable have reported a final weight between 613.3 a 631.4 kg, a 1.41 to 1.46 kg/d of ADG¹⁵, while a study carried out in Mexico found that Holstein steers reached a final weight of 604.9 kg with a daily gain of 1.46 kg and a feed consumption of 8.41 kg per day¹⁶, another study performed by Carvalho et al¹⁷ found that Holstein steers gained daily 1.73 kg/d with a final weight of 598 kg. Although in Mexico the federal norm³ establishes that pen space for an animal under 400 kg should be 12 m² and for one above 400 kg 20 m²². It may be expected that the world trend to reduce the space allowance per animal in cattle feedlot¹⁸ is impacting Mexico, so it is likely that welfare and production variables will be affected because of smaller allowed space for feedlot cattle.

Carcass and meat evaluation

The group of steers that was provided with the largest living space showed a difference of 7 kg both in the hot and cold carcass weight (P<0.05), these results are shown in Table 3 and correspond with it was reported by Ha et al¹³ who provided a greater living space to steers that were in the finalization period. A similar study¹⁹ reported a larger hot carcass weight for feedlot steers which were provided with 16 m²/animal, when compared with two other groups of animals that had a living space of 10.6 and 8 m²/animal.

In the present study dorsal fat and ribeye space showed no statistical difference between groups (P>0.05), this result corresponds to what is reported in Hanwoo cattle carcasses¹⁹. In contrast with this study, researchers²⁰ found no differences (P>0.05) between Hanwoo carcasses obtained from animals that were provided with different living spaces. Other authors have reported lower dorsal fat numbers, 5.15 mm¹⁴; 5.8 mm^17,21; while Carvalho et al¹⁵ reported a dorsal fat measurement between 8.6 and 9.3 mm, Torrentera et al¹⁶ observed a dorsal fat depth of 10.9 mm results that are similar to what was observed in the present study.

Authors have found that dairy cattle tend to deposit greater amounts of fat in the abdominal cavity and to accumulate less subcutaneous fat²², in this context bovine races that are bigger and take more time to mature have a larger proportion of inter and intramuscular fat when compared with smaller races which mature earlier²³.

In the case of ribeye area, the present study found that they were larger than the ones reported by Ha et al¹³ for Hanwoo steers (91.0 and 94.6 cm² for 10 and 16.7 m² of living space) likewise other studies in Holstein steers reported ribeye areas of 72.36 cm²¹⁷; 73.7 cm²²¹; 74.9-82.5 cm^{2 15}; 77.21 cm^{2 14}; 81.22 cm^{2 16}.

Regarding the amount of intramuscular fat in the meat (Table 4) the results indicate that there is no difference between the groups, however the findings support the reports from other researchers that in the case of Holstein steers choice beef is the grade that is observed^16,17,21. In this study, 130 of the steer’s carcasses produce beef that was classified as small while a second group of 159 carcasses yielded modest beef.

Table 5 show both groups physicochemical results, it was found that in the case of pH, L*, a* y C* no differences were observed (P>0.05), and although the values for b* y H* showed differences (P<0.05), this dissimilarity does not result in noticeable differences in color between treatments.

In regard to pH, values between 5.5 and 5.8 are considered as normal for bovine meat²⁴; so, the results obtained by the present study may be viewed as typical. Similar pH values and have been reported in studies done with Holstein by other authors^6,25. In the case of meat color, based in what has been reported by others authors²⁴, the meat obtained from both groups is considered as dark cutting, another research have reported similar results (L* =37.50, a*=14.69 y b*=12.39)²⁶ and (L*= 38.02, a*=19.86, b*=8.19, C*=21.49)¹⁴; the reason for this may be explained by the pre slaughter stress that the animals were submitted to, which depleted blood glycogen and affected the beef´s color²⁷. Authors have informed that the way animals are handled, the novelty of environment and fatigue, are factors that contribute to stress²⁸.