Strategic supplementation of bypass protein and fat to dual purpose cattle in the colombian tropics during the dry season

Strategic supplementation of bypass protein and fat to dual purpose cattle in the colombian tropics during the dry season

Héctor J Anzola, Germán Martínez, Fernando Gómez, Yesid Hernández and Hugoberto Huertas

Instituto Colombiano Agropecuario, Apartado Aéreo 151123
El Dorado, Bogotá, Colombia

The effect of strategic supplementation with bypass protein and fat to dual purpose cows (1/2 European; 1/2 Zebu) was studied from calving to 188 days of lactation, during the dry and beginning of the wet season in the Colombian tropics. Forty F1 cows of four breeding groups: Normandy x Zebu (N x Z = 14); Brown Swiss x Zebu (BS x Z = 10); Gyr x Holstein (G x H = 7) and Holstein x Zebu (H x Z = 9) grazing Brachiaria decumbens were supplemented with three levels of bypass protein (0, 0.5 and 1 kg dry matter per day) of Cotton Seed Meal (CSM) and a mixture of urea, sulphur and a combined source of protein, starch and oil (0.5 kg dry matter per day of rice polishing, RP); the control group grazed Brachiaria decumbens without supplements.

A positive (P<0.05) effect was observed in total and daily milk production due to supplementation. Cows in all treatments lost weight but those given zero CSM had the highest weight losses (-299 g/day) (P<0.05). Calves out of supplemented cows gained faster (P<0.05) and had heavier weaning weights (P<0.05) than calves in the control group. Gyr x Holstein F1 cows had significantly (P<0.05) greater total and daily milk production. Reproductive performance was significantly (P<0.05) better in all supplemented groups compared with the control group (66.7 vs 30% pregnancy rates). Normandy x Zebu and Holstein x Zebu averaged 74.6% pregnancy rate against 34.3% for Brown Swiss x Zebu and Gyr x Holstein cows. In conclusion, supplemented cows showed better total productive performance due to lower weight losses, higher milk production, better pregnancy rate and heavier calves.

Key Words: Brachiaria, bypass protein, dual purpose cattle, European x Zebu, rice polishing, cottonseed meal.

In the humid and sub-humid tropics of Colombia there is an increasing number of herds in which cows are milked and raise their calves simultaneously under grazing conditions only. This system of production is mainly exploited with crossbred European dairy breeds x Zebu or Criollo cows and is known as the Dual Purpose System. In the regions where this system is practised there is a lower availability of dry matter during the dry season, critical for those cows that are lactating and should re-conceive. It has been shown by Escobar (1988), Lindsay (1983) and Lindsay and Loxton (1981), that daily supplementation with 50 g fermentable N and 1.2 kg of a bypass protein meal increases the forage intake in pregnant or lactating cows. However, the optimum level of supplementation will be determined by relative needs for fermentable N and bypass nutrients and with the availability and quality of pasture.

The objective of this experiment was to determine the best level of supplementation for dual purpose cattle calving during the dry season.

The experiment was conducted at "La Libertad" Experimental Research Station of ICA (Instituto Colombiano Agropecuario) located in the foothills of Eastern Colombia, at 376 m above sea level, with 27°C annual mean temperature, 2800 mm rainfall and 87% relative humidity.

Forty F1 cows of four breeding groups: Normandy x Zebu (N x Z=14); Brown Swiss x Zebu (BS x Z = 10); Gyr x Holstein (G x H = 7) and Holstein x Zebu (H x Z = 9) were randomly alloted to four treatment groups from calving to 188 days of lactation, during the dry and beginning of the wet season, to measure the response in milk production, body weight change and weight gain of their calves when grazing Brachiaria sp. The treatment groups were:

C: Control group: no supplementation
URP: Urea (U = 60 g/animal/day); Molasses (M = 450 g/animal/day); Rice Polishing (RP = 500 g/animal/day).
URPCSML: U = 60 g/an/day; M = 450 g/an/day; RP = 500 g/an/day and 0.5 kg/animal/day of Cotton Seed Meal (CSM)
URPCSMH: U = 60 g/an/day; M = 450 g/an/day; RP = 500 g/an/day and 1.0 kg/animal/day CSM.

Daily milk production, body weight every 28 days, birth weight of calves and supplement intake were recorded in all cows and calves.

Statistical evaluation of the data was made by analysis of variance which included supplement, breeding group and their interaction. When differences were significant (P<0.05) all possible combinations of pair comparisons were tested by "t" test. (Steel and Torrie 1980). Since reproductive performance is a binomial (pregnant or not pregnant) rather than a normal distribution the Chi-square test was used for this parameter.

The data in Table 1 show the probabilities of attaining greater F values from analysis of variance of the traits studied. The supplement was a highly significant (P<0.01) source of variation for milk traits and average daily gain (ADG) of cows and (P<0.05) for calf ADG and final weight of cows and their calves. Breeding group affected (P<0.01) total milk production; daily milk production (P=0.07) and ADG (P=0.06) of cows approached significant levels at 5% of statistical probability. Supplement by breeding group interaction was the only significant source of variation (P<0.05) for ADG of cows.

Table 1: Probabilities of attaining greater F-values from analysis of variance for total and daily milk production, average daily gain and final weight of cows and calves supplement during the dry season.

Trait	Supplement	Breeding	S X BG	Error
	(S)	group (BG)

df	3	3	9	24
Milk production(kg)
- Total	0.01	0.01	0.77
- Daily	0.01	0.07	0.02
Daily gain
- Cow	0.01	0.06	0.02
- Calf	0.03	0.28	0.81
Final weight
- Cow	0.04	0.22	0.70
- Calf	0.03	0.18	0.67

Milk production during the total experimental period (188 days) is presented in Table 2. All supplemented groups had significantly (P<0.05) higher yields than the control group. The supplemented groups averaged 838 kg in the total period, which gives 4.5 kg per animal/day. This difference represents a 31% advantage over the control group (578 kg and 3.0 kg/day). This result may be due to better nutrient balance in the reticulum-rumen of the supplemented cows. According to Preston and Leng (1987) supplementation with bypass protein usually produces an increase in animal production.

Table 2: Total and daily milk production of dual purpose cattle supplemented during the dry season in the foothills of the Eastern plains of Colombia.

	No.	---------- Milk production (Mean±SE) ----------
	Cows	Total (kg)	Daily(kg/d)

SUPPLEMENT
Control	10	577 ± 64.7 a	3.0 ± 0.35 a
U-M-RP	10	790 ± 56.3 b	4.5 ± 0.31 b
U-M-RP-0.5 CSM	10	904 ± 61.5 b	4.8 ± 0.34 b
U-M-RP-1.0 CSM	10	819 ± 63.2 b	4.1 ± 0.35 b

CROSSBRED GROUPS
Normandy x Zebu	14	697 ± 49.0 a	3.6 ± 0.27 a
Brown Swiss x Zebu	10	698 ± 59.9 a	3.8 ± 0.33 a
Gyr x Holstein	7	1,047 ± 82.4 b	5.2 ± 0.46 b
Holstein x Zebu	9	648 ± 70.8 a	3.7 ±0.39 a

ab = Means without a common letter differ (P<0.05)
U-M: (Urea-Molasses): 60 and 450 g/animal/day
RP: (Rice Polishing): 500 g/animal/day
CSM: (Cotton Seed Meal): 0.5 and 1.0 kg/animal/day

There was a significant (P<0.05) effect of breeding group on total milk production. Gyr x Holstein F1 (G x H) cows produced 1047±82 kg (5.2±0.46 kg/day) of milk which is 35% more than the average of the other groups. This result could be due to the higher additive effect (Syrstad 1985) of the Gyr x Holstein cows which were obtained out of purebred Holstein cows and an outstanding dairy Gyr bull. European x Zebu cows of the other groups (Holstein x Zebu) (H x Z); (Brown Swiss x Zebu) (BS x Z) and (Normandy x Zebu) (N x Z) were obtained out of commercial Zebu (Brahman) cows from beef herds, so aditive effects for increased milk production are expected to be of lower magnitude than in the (G x H) group.

The data in Table 3 are the average daily changes in liveweight of the cows. All cows were losing weight. Those in the supplemented groups with 0.5 and 1.0 kg/day of CSM had the smallest losses (-64 and -32 g/day), were the heaviest at the end of the experimental period and produced much more milk than the other groups (Table 2). The above results can be explained by the different levels of fermentable N, the bypass of fat and protein to the intestinal tract (Lindsay and Loxton 1981; Lindsay 1983). Lindsay et al (1982) considered that the greater weight gain of supplemented cows is due to the increased intake of the basal diet when this is composed of grasses of low to medium nutritive value.

Table 3: Average daily gain (ADG) and final weight (FW) of crossbred dual purpose cows supplemented during the dry season in the foothills of Eastern plains of Colombia.

	No	ADG	Final weight
	Cows	(g/day)±SE	kg±SE

SUPPLEMENT
Control	10	-123 ± 64 a	402 ± 18.4 a
U-M-RP	10	-299 ± 56 b	390 ± 16.0 a
U-M-RP-0.5 CSM	10	-64 ± 61 a	461 ± 17.5 b
U-M-RP-1.0 CSM	10	-32 ± 63 a	422 ± 18.0 ab

CROSSBRED GROUPS
Normandy x Zebu	14	-28 ± 48 a	435 ± 13.9 a
Brown Swiss x Zebu	10	-76 ± 59 a	391 ± 17.0 b
Gyr x Holstein	7	-164 ± 82 ab	440 ± 23.5 a
Holstein x Zebu	9	-250 ± 71 b	409 ± 20.1 a

Normandy x Zebu cows lost less weight than (G x H) and (H x Z) cows (P<0.5). (N x Z) cows have less genetic potential to produce milk since the Normandy breed has been selected to be a double utility animal (beef and milk) so probably has more ability to gain weight than those cows which are from breeds that have had higher selection pressure for milk production as is the case for the Holstein and Brown Swiss breeds.

Significant differences (P<0.05) were found in the ADG of calves out of cows that received the supplements. On the average, calves whose dams were supplemented gained 475 g/day, which is 139 g/day more than for calves in the control group. As a result their final weight was higher than those in the un-supplemented group (Table 4). Calves out of Brown Swiss x Zebu cows had the lowest daily gains and final weight.

Even though the analysis of variance did not show statistical differences (P>0.10), the "t" test showed significant (P<0.05) differences between the calves out of Brown Swiss x Zebu cows compared with calves out of the other three crossbred groups (358 vs 468 g/day) which did not differ (P>0.10) among themselves.

There was a significant correlation (r= 0.77; P<0.05) between milk production and ADG of calves. Cows receiving supplements produced more milk of superior composition (fat, protein and lactose) than un-supplemented cows.

Table 4: Average daily gain (ADG) and adjusted 240-day weight (FW) of calves out of F1 crossbred dual purpose cows supplemented during the dry season in the foothills of Eastern plains of Colombia.

	No	ADG	Final weight
	Cows	(g/day)±SF	(kg)±SE

SUPPLEMENT
Control	10	336 ± 46 a	112 ± 11.5 a
UM-RP	10	420 ± 40 ab	133 ± 9.9 a
UM-RP-0.5 CSM	10	463 ± 49 b	147 ± 12.1 b
UM-RP-1.0 CSM	10	542 ± 46 b	163 ± 11.2 b

CROSSBRED GROUPS (COWS)
Normandy x Zebu	14	466 ± 35 a	144 ± 8.8 a
Brown Swiss x Zebu	10	358 ± 51 b	115 ± 12.7 b
Gyr x Holstein	7	468 ± 60 a	147 ± 14.8 a
Holstein x Zebu	9	470 ± 51 a	149 ± 12.7 a

Calves from cows that received the more complete supplements (treatments URPCSML and URPCSMH that contained cottonseed meal) were significantly (P<0.05) heavier (156 kg) than those in the control and URP groups (123 kg). The lightest weight was obtained for calves out of cows in the control group. Calves out of BS x Z cows were also the lightest (P<0.05). The heaviest calves were those from cows receiving the best supplement (1.0 kg of CSM). This seems to be a logical result since this treatment would have resulted in the best balance of nutrients. Besides, according to Preston (1983), the superior composition of milk from supplemented cows is likely to act synergistically so as to improve the overall utilization of all the diet.

According to Maijala (1978) reproduction is the most important trait to consider when aiming to improve animal production. A highly significant effect (P<0.05) was found as a consequence of the supplementation of cows. Since there were no statistical differences among supplemented groups (P>0.10) data were pooled and a Chi-square test was used to assess the relationship between the supplement and pregnancy rate. The pooled chi-square value was 4.13 (P<0.05).

The pregnancy rate of cows in the supplemented groups (Table 5) averaged 67% in the 120 days of the mating season from March to July. The mating season was suspended 60 days prior to the end of the experiment.

Table 5: Reproductive performance of crossbred dual purpose cows supplemented during the dry season in the foothills of Eastern plains of Colombia.

	No	No	Pregnant
	Cows	Pregnant cows	percentage

SUPPLEMENT
Control	23	3	30.0 a
UM-RP	10	6	60.0 b
UM-RP-0.5 CSM	10	7	70.0 b
UM-RP-1.0 CSM	10	7	70.0 b

		Chi- square*	4.13**

CROSSBRED GROUPS
Normandy x Zebu	14	10	71.4 b
Brown Swiss x Zebu	10	4	40.0 a
Gyr x Holstein	7	2	28.6 a
Holstein x Zebu	9	7	77.8 b

		Chi-square*	6.27 ***

Among breeding groups there were significant differences (Chi-square value was 6.27 (P<0.10)) for (N x Z) and (H x Z) crosses which had higher reproductive performance than (BS x Z) and (G x H) cows. The poor performance of (G x H) F1 cows could be due to their higher milk production (Everet et al 1966). On the other hand, (BS x Z) cows have been reported to have poorer reproductive performance than other types of F1 crosses (Vaccaro 1984).

In order to combine in an index the reproductive and productive performance of cows, the total milk production, in 188 days of lactation, was divided by five to make it equivalent to 1 kg of meat produced by the calf. To this was added the weight (kg) of the calves and the final figure was corrected for the metabolic body weight of the cows (W^0.75). It can be seen (Table 6) that supplemented cows were more efficient (P=0.06) than those in the control group (3.08 vs 2.38). Among the supplemented groups there were no statistical differences (P>0.10). However, the response to the different levels of supplementation was linear (r=0.92).

Even though (G x H) cows were the heaviest, due to their higher milk production (1047 kg) and good final weight of their calves (147 kg), they had the highest value in efficiency of total production related to their metabolic weight. (H x Z) cows ranked in second place without any statistical difference (P>0.05) between them and (G x H) F1 cows. There were no statistical differences (P>0.05) between (N x Z) (2.69) and (BS x Z) (2.66) cows.

Table 6: Ratio of production efficiency [(Milk/5 + calf weight)/ cow metabolic weight].

	No. Cows	(Milk/5 + Calf weight)/Cow LW^0.75

SUPPLEMENT
Control	10	2.38 ± 0.22 a
UM-RP	10	2.99 ± 0.19 b
UM-RP-0.5 CSM	10	3.02 ± 0.23 b
UM-RP-1.0 CSM	10	3.22 ± 0.22 b

CROSSBRED GROUPS
Normandy x Zebu	14	2.69 ± 0.17 a
Brown Swiss x Zebu	10	2.66 ± 0.25 a
Gyr x Holstein	7	3.52 ± 0.29 b
Holstein x Zebu	9	2.74 ± 0.25 ab

Several positive biological effects were found as a result of supplementation of dual purpose F1 cows. Supplemented cows showed a very good total productive performance. They had lower weight losses, higher milk production and pregnancy rate than un-supplemented cows. Their calves gained faster from birth to 188 days of age and consequently were heavier than those out of un-supplemented cows. It can be concluded, because of the good performance of (G x H) cows, that besides heterotic effects through crossing European with Zebu breeds, it is important to exploit breed complementarity using the additive effects by the use of superior animals in the crossbreeding plan.

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