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Lactation Curves for First Lactation Egyptian Buffalo
Lactation Curves for First Lactation Egyptian Buffalo G. H. METRY and K. A. MOURAD Animal Production Research Institute Agriculture Research Center Ministry of Agriculture Giza, Egypt
J. C. WILK and B. T. McDANIEL Department of Animal Science North Carolina State University Raleigh 27695-7621 ABSTRACT
First lactation records of 1538 buffalo maintained at the Animal Production Research Institute fanns in 1967 to 1990 were used to determine lactation curves for three lactation lengths: >28 and <150 d, >149 d, and ~308 d, as well as all records. Daily milk yields were summed by 14-d intervals for analyses. Yields peaked at the first, fifth, sixth, and seventh periods for >28 and <150 d, >149 d. ~308 d, and all records. Herd-yearseason significantly affected milk yield in all periods. Persistency for all records and three groupings (>28 d, >149 d, and ~308 d in milk) was highest for the ~308-d group (1.02 vs..85 for >149 d, .57 for >28 d, and .47 for all records). Herd-year-season of calving significantly affected persistency in all records and the three subset groupings. Persistency was higher for buffalo calving in spring and summer for all records, records >28 d, and records> 149 d but in summer and autumn for the ~308 d records. In records ~308 d, the correlation coefficient between persistency and milk yield (r = .06) was not significant but was negative with season of calving (r = -.11).
(Key words: buffalo, first lactation, curve) INTRODUCTION
Buffalo (Type Beheri of genera Bubalis) are considered to be the principal milk-yielding
Received July 2, 1993. Accepted December 22. 1993. 1994 J Dairy Sci 77:1306-1314
species in Egypt and provide milk and milk products that are important sources of protein, energy, vitamins, and minerals for the diet of the Egyptian people. However, the amount of milk yield in Egypt is inadequate to meet the needs of the people there. A better understanding of factors influencing yield of buffalo is needed to increase the total amount of milk produced in Egypt. Animal health, feeding, and reproductive programs and their management account for 75% of variation in herd yield, and the remaining 25% is due to genetic sectors (3). The rate of secretion of milk in dairy animals displays a definite trend throughout the lactation period. Following parturition, daily milk yield increases to a peak and then gradually declines until the lactation is ended. Some lactations are terminated or truncated before the desired time (usually 305 d) because of low persistency (6). The shape of the lactation curve is influenced by parity and season of calving in cattle (25). Fann, parity, and season of calving influenced the shape of lactation curve of Egyptian buffalo (16). Qualitative and quantitative differences in feeding and management are among the important causes of variation in milk yield (18) and greatly influence the shape of the lactation curve. The shapes of lactation curves could be measured by the persistency of yield [i.e., the ratio of yields in consecutive periods (4)]. Maymone and Malossini (11) estimated the persistency of milk yield in buffalo as the ratio of amount of milk produced in the second 100 d of lactation to that produced in the first 100 d of lactation. Most studies of milk yield of buffalo have used only lactations of ~305 d (1, 17), but some have used lactations >150 d (16). The objectives of this study were to investigate the effects of herd-year-season and age at calving on the shape of the production curve
1306
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LACTATION CURVES
of first lactation buffalo and their persistency in lactations of different lengths. MATERIALS AND METHODS
Daily milk yield records were available from 1538 first lactation buffalo calving from 1967 to 1990 in herds at three experimental stations of the Animal Production Research Institute, (El-Nattaf EI-Gedid, EI-Nattaf EIKadem, and Mehallet Mousa, Egypt). The herds were maintained according to feeding and management standards adopted by the institute. During winter and spring (December to May), cows were grazed on Egyptian clover as the only source of feed. During summer and autumn (June to November), cows were kept under open sheds covered with asbestos roofs 4 m high. During this period, feeding consisted of a concentrate mixture, wheat or rice straw, and a limited amount of clover hay when available. The cows were milked by hand twice daily at 0730 and 1630 h without the presence of the calf. In order to include all possible variations in the shape of lactation curve, records were included whether or not 308 d of lactation were completed. Preparatory to this study, the daily milk yields were summed by l4-d intervals for the duration of the lactation. A total of 498 of the 1538 records had <29 d of lactation and were deleted from some analyses because of problems occurring before, at, or just after parturition. The remaining records were then sorted into four groupings: 1040 lactations >28 d, 344 lactations >28 and <150 d, 651 lactations >149 d, and 260 lactations ~308 d (22 periods) (Table I). The subsets were for estimation of
persistency of lactations of variable length >28 d, intennediate length> 149 d, and those ~308 d. Lactations >28 d included those >149 d, and those >149 d included those ~308 d. All records were used to detennine the pooled lactation curve with the following model using software of SAS (19). Yijklm
Record length (d)
(n)
>28 >28 and <:150 1 >149
1040 344 651
~308
260
Total
1538
(kg)
892 360 1229 1661 606
[1]
where Yijklm {30
HYSi bl ~
b3 Pj Pk PI eijklm
= 14-d milk yield = intercept, = random effect
record,
of herd-yearseason i, = partial linear regression of milk yield on stage of lactation (period), = partial quadratic regression of milk yield on (stage)2, = partial cubic re¥ression of milk yield on (stage) , = stage of lactation j (j = I, 2, 3... ,22), = (stage)2, = (stage)3, and = a random residual, normally and independently distributed with · 2 zero mean and vanance (Je'
The records of the three groups based on lactation length (>28 d but <150 d, >149 d, and ~308 d) were used to detennine the lactation curves. The three subsets were analyzed as follows.
= {30
+ HYSi + b 1(Gj x Pk) + b2(Gj x + b3(Gj x P~) + eijklmn
Lactation length (d)
+ HYSi + bl(Pj) + b2(P~)
+ b3(P~) + ~jklm
TABLE I. Mean milk yield and lactation length in the three different groupings and all records. Mean milk yield
= (30
ph
[2]
where
212
88 290 393 144
Yijklmn (Gj x Pk)
= 14-d milk yield record, = stage of lactation k (k = 1,2,...22) within group j (j = 1,2,3),
lThe group included to draw a separate curve. Journal of Dairy Science Vol. 77, No.5, 1994
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METRY ET AL.
(OJ x P~)
= (stageY
(OJ x P~)
= (stage)3
within group,
A2
within group,
A3
k I
and other descriptions are as in Model [I]. To determine the lactation curves by season of calving from all records, the following model was used. Yijklmn
= 130
+ HYj + bl(Sj x Pk) + b2(Sj x + b3(Sj x P~) + eijklmn [3]
ph
= (ageY. = (age>3,
and other descriptions are as in Model [I]. The effect of age at calving on milk yield by stage of lactation by season was calculated from the following model. Yijldmn
= f30 + HYi + Sj + bl(~) + b2(Ah + b3(A~) + b4(Sj x Ak)
+ bs(Sj x Ar) + b6(S x A3) + eijldmn [5]
where Yjjklmn HYj bl
= 14-d milk yield record, = random effect of herd-year i, = partial linear regression of
where 14-d milk record, season j of calving, partial linear regression of milk yield by stage on age at calving. b2 = partial quadratic regression of milk yield by stage on (ageY, b3 = partial cubic regression of milk yield by stage on (age)3, b4 = partial linear regression of milk yield by stage on age at calving by season, bs = partial quadratic regression of milk yield by stage on (ageY by season, b6 = partial cubic regression of milk yield on (age)3 by season, Ak = age k at calving in mo, = (ageY,
milk yield on stage within season, b2 = partial quadratic regression of milk yield on (stageY within season, b3 = partial cubic regression of milk yield on (stage)3 within season. (Sj x Pk) = stage of lactation k within season j of calving, [1 = spring (March to May), 2 = summer (June to August), 3 = autumn (September to November), and 4 = winter (December to February)], (Sj :-: = (stageY within season,
ph
(Sj x P 3) m
= (stage)3
within season, and
with f30 and eijldmn as described earlier. The effect of age at calving on milk yield for each stage of lactation (14 d milk yield) was obtained from the following model. Yijklm
= 130
+ HYS j + bl(Aj) + ~(A~)
+ b3(A?) + ~jklm
[4]
where Yijklm Aj
= 14-d milk record, at calving in G = 27,28,.... ,77),
= age j
months
Journal of Dairy Science Vol. 77, No. S. 1994
Ar
3 Am
= (age)3,
(Sj
x Ak) = age k at calving by season j, x Ah = (ageY by season.
(Sj
x A~)
(Sj
= (age>3
by season,
and other descriptions are as in Model [4]. Persistencies in all records and the three classes (>28, >149, and ~308 d of lactation) were each estimated as the ratio of milk yield in the second 100 d of lactation to milk yield in the fIrst 100 d of lactation (P2:1) (11) using Model [6],
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LACTAnON CURVES
Yijklmn =
t30 + HYi + Sj +
bl(~)
+ b2(Ar> + b3(A~) + b4(Sj x Ak)
+ bs(Sj x
At> + b6(S x
A3)
+ eijklmn
[6] Periods 2 in lactation
where Yijklm
TABLE 2. Regression of milk yield! by 14-d periods on age at calving, (age)2, (age)3, and percentage of variance due to age at calving within herd-year-season (HYS) for first lactation buffalo.
= the
persistency percentage,
and other descriptions are as in Models [4] and [5]. RESULTS AND DISCUSSION
The mean milk yield, lactation length, and numbers of records for the subsets and overall records are given in Table l. Of the total records, 32% were <29 d and were excluded from analyses because of problems before, at, and after parturition (abortion, stillbirth, or failed to lactate). Only 16.9% of the 1538 fIrst lactation buffalo completed lactations that were ~308 d in length. The mean milk yield was nearly doubled, from 892 kg for the 1040 records >28 d to 1661 kg for the 260 records ~308 d of lactation. Also, the mean lactation length increased from 212 to 393 d for the respective groups of records.
Age
(Age)2
(Age)3
12.9** 14.7** -9.7 -14.1 -3.9 -8.8 -10.7 -197 -10.2 -7.4 -10.9 -14.7 -13.8 -14.9 -16.9 -6.2 -18.5 1.0 -3.9 5.3 .8 6.8
-.28** -.33**
.002** .002** -.002 -.003 -.001 -.002 -.002 -.003 -.002 -.001 -.002 -.003 -.003 -.003 -.003 -.001 -.003 .001 -.001 .001
Variance due to age within HYS (%)
I
2 3 4 S 6 7 8 9 10 II 12 13 14 IS 16 17 18 19 20 21
22
.22 .36 .11
.23 .25
.46 .26 .18
.27 .36 .33 .36 .40 .13
.44 -.04 .08 -.12 -.03 -.15
.000
.001
.79 .38 .32 .53 .64
.66 .41 .76 .24 .56 .75 .48 .90 .61 .75 .52 .82 1.13 1.03 1.96 1.94 1.27
**p < .01. lAdjusted for HYS. 214-d Milk yield.
Effect of Age at Calving
Regressions of milk yield (adjusted for herd-year-season) from Model [4] by 14-d periods on age, (ageY, and (ageY at calving and percentage of variance because of age at calving within herd-year-season from Model [4] are in Table 2. The effects of age at calving, (ageY, and (age)3 were signifIcant (P < .01) for the first and second periods but not for periods 3 through 22. This result agrees somewhat with results of Singh and Yadav (20), who reported that mean milk yield by Murrah buffalo in India was not affected by age at fIrst calving. The percentage of variance because of age at calving within herd-year-season was small «1%) for early stages but increased to 1.27 by period 22 (Table 2). The effects of herd-year, season, and age at calving from Model [5J are shown in Table 3. Herd-year had a signifIcant effect (P < .01) on periods 1 through 16 (Table 3) but was not significant from periods 17 to 22. The herd-
year effect reflected the fluctuation in feed supply between years that was due to climatic conditions. These results are similar to those obtained in other studies of buffalo (16,20,24) and cattle (9, 22), but disagreed with observations by Khosla et al. (7), who reported that year of calving had no signifIcant effect on daily milk yield of first lactation buffalo in Pakistan. Their fIndings might have been influenced by the few years (1978 to 1980) covered by their study. Season of calving (Model [5]) was not significant for the 22 periods in milk. However, age at calving, (ageY, and (age)3 were significant (P < .01) in periods 1, 2, and 4 but not significant in periods 3 and 5 through 22 (Table 3). The percentage of variance because of periods within season was very small, .004, but was .11 for periods within herd-year. The Journal of Dairy Science Vol. 77, No.5, 1994
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METRY ET AL.
TABLE 3. Analysis of variance for factors affecting stage of lactation (14 d of lactation). Lactation periods l Source
df
Herd-year Season Age at calving (Age)2 (Age)3 (Age) x season (Age)2 x season (Age)3 x season
49 3 1 I 1 3 3 3
4
2
3
5.8** 1.1 3.3 t 2.91 2.4 1.1 1.1 1.0 18
3.3** 1.4 1.9 1.5 1.2 1.3 1.2 1.1 16
5 to 16
17 to 22
1.3 - 2.0** NS NS NS NS NS NS NS 14 - 18
NS NS NS NS NS NS NS NS IS - 23
F-value
R2, %
4.2** 1.1 8.8** 7.9** 7.0** 1.1 1.2 1.2 17
3.1** 1.3 2.7 3,P 3.6 t 1.3 1.3 1.3 16
1I4-d Milk yield,
tp < .10. *p < .05. "p < .01.
effects of age at calving, (ageY, and (ageY within season were not significant for all periods. Periods in milk were affected by factors other than season and age at calving, such as feeding, managerial practices, or the weather. Cockrill (4) reported that the effect of temperature and humidity were of great importance for milk yield in buffalo. Buffalo are more sensitive than cattle to heat exposure. As environmental temperatures rose, water consumption increased, but, if the feed intake was depressed, milk secretion decreased. Misra et al. (14) found that both food and water intakes in buffalo were reduced by ambient temperatures >32°C. Our findings agreed with those for Sahiwal cows of India (2) where season of calving had no significant effect on the weekly milk yield in the last few weeks of lactation. For Egyptian buffalo, Alim (1) and Salem (17) found that 305-d milk yield in multiple lactations of buffalo was not affected by season of calving. However, the results were not similar for Egyptian buffalo (5, 14) and for buffalo in Pakistan (7). Proportions of variance within the 22 periods attributable to the fifth analytical model ranged from R2 = .11 to .30 (fable 3). The contribution of herd-year to total variance within periods was 10 to 17%. These are less than the 30 to 38% of the total variance in milk yield by cattle in Brazil (12). The percentage of variance attributable to season of calving was relatively small at .54%. Journal of Dairy Science Vol. 77. No. S. 1994
lactation Curves
The estimates obtained from Model [1] were used to locate the points of the pooled curve (Figure 1). Estimates from Model [2] were used to obtain overall curves of expected yield for periods 1 through 12 for records >28 but <150 d and 22 for records >149 d and ~308 d (Figure 2). The pooled curve peaked at periods 7 and 8, decreased steadily until period 19, and then increased to period 22. The configuration of the lactation curve of records >28 but <150 d reached its peak at period I, main-
l00r--------------~
,...
80
20f-
4
6
8
10
12
14
16
18
20
22
p.,locta
Figure I, Overall lactation curve over 22 14-<1 periods for first lactation buffalo.
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LACTATION CURVES 100,-----------------,
100'1- - - - - - - - - - - i
80
:: -g
60
'iia. '6
:!..
40
:!!
E
20
20
\
~ I
oLI2
4
6
8
10
12
14
16
18
20
22
2
periods
_ 4
6
8
10
12
14
16
18
20
22
periods
Figure 2. Lactation curves over 22 14-d periods for flrstlactation buffalo with >28 d (0), >149 d (+), and ~308 d (.) of lactation.
Figure 3. Lactation curves over 22 14-d periods for seasons of calving spring summer (+). autumn (.), and winter (0) for first lactation buffalo.
tained this peak for three additional periods, and decreased rapidly until period 12, which reflected the low persistency. Records >149 d and ~308 d peaked at periods 5 and 6, respectively, and remained near the same level through periods 6 and 8 and then decreased until periods 21 and 22. The rate of decline in milk yield from the peak period to the next one was 5.0, 1.4, 1.3, and 1.5% for records >28 but <150 d, >149 d, >308 d of lactation, and all records, respectively. The mean rate of decline from the peak to period 12 was 22.1 % for records >28 but <150 d, but was only 3.1,2.8, and 1.3%, respectively, from peak to period 22 for records >149 d, ~308 d, and all records. Rates of decrease were less than reported for crossbred cattle in India (15). The rapid rate of decline in records >28 but <150 d and records >149 d was probably due to the short lactation records included, which terminated before 308 d of lactation. This result agrees with that of Singh et a1. (22), who reported that short lactations «305 d) were more common than long lactations (>305 d) for all parities of Murrah buffalo (956 short lactations out of 1609 records). Milk yield curves (Model [3]) for lactations initiated by calvings in the same season within herd-year are shown in Figure 3. The shape of the yield curve following winter calvings (December to February) was quite different from those of other seasons. The peak was similar to that for the other calving seasons. The ascend-
ing phase was seven periods; then yield declined rapidly from periods 8 to 19 and increased again from periods 20 to 22. Lactation rates following spring, summer, and autumn calvings remained at near peak levels for 2, 3, and 2 periods and declined steadily thereafter until periods 19, 21, and 22, respectively. The yield trend for winter calving was influenced between periods 8 and 19 by changes from winter feeding regimens (surplus energy and protein for milk yield from green clover, and mild weather) to summer feeding regimens (dry feed with high fiber and deficient protein, heat stress, and abrupt change from green to dry feed) and increased again at the beginning of the next winter season. This result agrees with reports that the differences in lactation curves of Flekvieh cattle in Hungary between calving seasons reflected differences in feeding (8). The trend following winter calvings agreed with that for imported Friesian cattle in Nigeria (23). Also, Madalena et al. (10) reported significant season effects on the parameters of the lactation curves of Holsteins in Brazil. Cows that calved in the wet season in Brazil had higher initial yield but were less persistent than those cows calving in the dry season.
e-).
Persistency
Persistencies (Model [6]) of milk yield as the ratio of the second 100 to the first 100 d of milk yield are presented in Table 4. The records with ~308 d of lactation had 102% Journal of Dairy Science Vol. 77. No. S. 1994
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METRY ET AL.
TABLE 4. Least squares means and standard errors for persistency! of first lactation buffalo calving in different seasons. Lactation records Items
>28 d
All records
X
SE
X
SE
X
SE
X
SE
.57 .62
.13 .03 .04 .03 .03
.85 .88 .89 .87
.11 .03 .03 .03 .02
1.02 1.01 1.11 1.06 .90
.10 .03 .04 .03 .03
.46 .52 .54 .41 .38
.10 .03 .03 .03 .03
Overall Spring Summer Autumn Winter 1A
>149 d
.64 .54 .48
.77
ratio of the second 100 and first 100 d of lactation.
persistency compared with persistencies of 85% in lactations >149 d, 57% in lactations >28 d, and only 46% in all records. A similarly calculated persistency of 83% was reported for first lactation buffalo in Italy (4). Records ~308 d of lactation had information in all periods, but records >28 d, >149 d, and all records had substantial numbers of records terminated earlier than 308 d of lactation. In addition, a higher proportion of the records in the >28 d, >149 d, and all records lactation groupings may have been influenced by poor design and management of health, nutrition, feeding, and reproduction programs. Also, lactations were terminated early because buffalo in poor condition at calving were unable to maintain acceptable milk yield. Mean persistencies for cows calving in spring, summer, autumn, and winter calvings
in records ~308 d of lactation were 10 I, Ill, 106, and 90%, respectively. Trends were similar for lactations >28 d, >149 d, and all records even though persistency was much lower. The similarity of trends indicates that the seasonality of production may be stimulated by the net effect of the season of year in which parturition occurred (16). The season stimulus is a consequence of nutrition, health, and climate and shows its influence at all stages of the lactation. Herd-year had a highly significant effect (P < .01) on persistency for all records, those >28 d, and those >149 d, and this effect was significant (P < .05) for the ~308-d grouping (Table 5). Season of calving affected (P < .05) the persistency of all records and of records >28 d (P < .01). Season was significant (P < .10) for records ~308 d but not for records
TABLE 5. Analysis of variance for persistencyl of lactation milk yield for records >28 d, >149 d,
df 49 3 1 1 1
984
>149 d
MS
df
1.15 u
.16 28.9
MS .18-.12
47 3
1.19-.30 .30 .27
4 4 4 588
.12 .12 .18* .07 222
!A ratio of the second 100 and first 100 d of lactation.
tp < .10. -p < .05. up < .01. Journal of Dairy Science Vol. 77. No.5, 1994
All records
MS
df
MS
28 3 1 1
.05.o7 t .16.17-
49 3
2.17-.39*
3 3
.06 .06
4
.30 t
220
.03 30.4
1481
.14 35.7
LACTATION CURVES
>149 d of lactation. These findings were similar to those of Zamorano Villarreal (26) with Friesian cows in Mexico. Age at calving had significant linear and quadratic effects (P < .05) on the persistency in ~308-d records but was not significant in >28-d records (Table 5), which agrees with findings (26) for cattle. This discrepancy could be explained by the wide variation in age at calving (27 to 77 mo) in the >28-d grouping; consequently, persistency varied. Correlation was positive but not significant between persistency and 308-d milk yield (r = .06), but negative between persistency and season of calving (r = -.11). However, the magnitude of correlation between persistency and milk yield was less than for first lactation Holstein-Friesians (r .35), which disagrees with Zamorano Villarreal (26).
=
CONCLUSIONS
Factors affecting the shape of lactation curves of buffalo are likely similar to those of cattle. A high percentage of the first lactation buffalo in this study had short lactations (37.4% had <150 d of lactation). Short lactations and the consequent low yearly milk yields drastically reduce the usefulness of buffalo as dairy animals. More research to identify the underlying genetic and environmental causes should be a high priority for areas where dairy buffalo are used. Seasonal differences suggest that improved management through adequate feeding for milk yield, disease prevention, parasite control, protection against extremes of climate, and a regular reproductive timetable could be useful to improve milk yield.
REFERENCES I Alim, K. A. 1978. The productive perfonnance of Egyptian buffalo in dairy herd. World Rev. Anim. Prod. 14:2. 2 Biswas, J. C., G. L. Koul, M. Kumar, P. N. Bhat, and G. Sing. 1986. Effect of non-genetic factors on weekly milk yield in Sahiwal cows. Indian 1. Anim. Sci. 56:1165. 3 Brackett, B. G., G. E. Seidel, Jr., and S. M. Seidel.
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1981. New Technologies in Animal Breeding. Academic Press, New York, NY. 4 Cockrill, W. R. 1974. The Husbandry and Health of the Domestic Buffalo. Food Agric. Organization U. N.• Rome, Italy. 5 EI-Irian. M. A. 1981. Studies on milk production of Egyptian buffaloes. M.Sc. Thesis, Fac. Agric., Univ. El-Mansourah, Mansourah, Egypt. 6 Gilmore, L. O. 1952. Environmental factors affecting production. Dairy Cattle Breeding. R. W. Gregory. ed. J. B. Lippincott Co., Philadelphia, PA. 7 Khosla, S. K., S. S. Gill, O. S. Pannar, and P. K. Malhotra. 1985. Factors affecting peak yield and yield per day of lactation in buffaloes under field conditions. 1. Res. Punjab Agric. Univ. 22:747. 8 Komarek, L., and A. Ruegsegger. 1986. Lactation curve for milk yield and milk composition. Simmentaler Fleclcvieh. 4: 14. 9 Lee, J. K., and B. K. Ohh. 1986. Importance and relative magnitude of environmental factors for milk yield in Korea dairy cattle. Korean J. Anim. Sci. 56: 1165. 10 Madalena, F. E., M. L. Martiz, and A. F. Freitas. 1979. Lactation curves of Holstein-Friesian and Holstein-Friesian x Gir cows. Anim. Prod. 29:101. II Maymone, B., and F. Malossini. 1961. Lactation curve in buffalo cows. Ann. 1st. Spero Zootec. Roma 8:3. 12 McDowell, R. E. 1983. Strategy for improving beef and dairy cattle in tropics. Cornell Int. Agric. Mimeo 1001. Cornell Univ., Ithaca, NY. 13 Misra, M. S., B. P. Sengupta, and A. Roy. Physiological reactions of buffalo cows maintained in two different housing conditions during summer months. Ind. 1. Dairy Sci. 16:203. 14 Mourad, K. A., E. A. Afifi, and L. H. Bedeir. 1990. Non-genetic factors influencing milk production traits in Egyptian buffaloes. Egypt. J. Anim. Prod. 27:1. 15 Patel, J. M., A. M. Patel, and A. D. Dave. 1989. First lactation trend in Jersey x Kankrej and Holstein x Kankrej FI crossbred. Indian J. Anim. Sci. 59:162. 16 Ragab, M. T., A. S. Abdel-Aziz, and A. Kamal. 1973. Effect of fann, parity and season of calving on the lactation curve in buffaloes. Egypt. 1. Anim. Prod. 13: 123. 17 Salem, A. Y. 1983. Effect of non-genetic factors on milk yield of buffaloes in Egypt. M.Sc. Thesis, Fac. Agric. Tanta Univ .• Kafr EI-Sheikh, Egypt. 18 Sandra. A. Q., M. A. Giannoni, A. A. Ramos, and H. Tonhati. 1987. Environmental effects on the variation of productive traits in Holstein-Friesian x Zebu crossbred cattle in the region of Sao Carlos, state of Sao Paulo, Brazil. I. Milk yield. Rev. Brasl. Genet. 5: 63. 19 SAS~ User's Guide: Statistics, Version 6.03 Edition. 1988. SAS Inst., Inc., Cary, NC. 20 Singh, C. V., and M. C. Yadav. 1987. Non-genetic factors affecting daily milk yield in Murrah buffaloes. Indian 1. Anim. Sci. 57 :56. 21 Singh, R. V., D. K. Sadana, and S. S. Tomar. 1988. Nature and distribution of the short and long lactations in buffaloes. Buffalo J. 4:85. 22 Thomas, P., S. Iype, E. Luiting, and H. Bakker. 1987. Journal of Dairy Science Vol. 77, No.5, 1994
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Factors affecting first lactation milk yield in Brown Swiss crossbred cattle under field conditions in Kerala. Indian J. Anim. Sci. 57:331. 23 Udedibie. A.B.I.. I. Umo. and I. Shaibu. 1985. The Vomherd. II. Effect of lactation number and season of calving on lactational characteristics of imported Friesian cows. J. Anim. Prod. Res. 5:31. 24 Vij. P. K. 1986. Phenotypic and genetic parameters of
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some production traits in buffaloes. Indian Vet. J. 63: 838. 25 Wood. P.D.P.• 1969. Factors affecting the shape of the lactation curve in cattle. J. Anim. Prod. 11 :307. 26 Zamorano Villarreal. H. E. 1986. Quantitative analysis of lactation curve up to the 5th calving in commercial herd of Holstein-Friesian cows. Veterinaria (Mex. City) 17:133.
J. C. WILK and B. T. McDANIEL Department of Animal Science North Carolina State University Raleigh 27695-7621 ABSTRACT
First lactation records of 1538 buffalo maintained at the Animal Production Research Institute fanns in 1967 to 1990 were used to determine lactation curves for three lactation lengths: >28 and <150 d, >149 d, and ~308 d, as well as all records. Daily milk yields were summed by 14-d intervals for analyses. Yields peaked at the first, fifth, sixth, and seventh periods for >28 and <150 d, >149 d. ~308 d, and all records. Herd-yearseason significantly affected milk yield in all periods. Persistency for all records and three groupings (>28 d, >149 d, and ~308 d in milk) was highest for the ~308-d group (1.02 vs..85 for >149 d, .57 for >28 d, and .47 for all records). Herd-year-season of calving significantly affected persistency in all records and the three subset groupings. Persistency was higher for buffalo calving in spring and summer for all records, records >28 d, and records> 149 d but in summer and autumn for the ~308 d records. In records ~308 d, the correlation coefficient between persistency and milk yield (r = .06) was not significant but was negative with season of calving (r = -.11).
(Key words: buffalo, first lactation, curve) INTRODUCTION
Buffalo (Type Beheri of genera Bubalis) are considered to be the principal milk-yielding
Received July 2, 1993. Accepted December 22. 1993. 1994 J Dairy Sci 77:1306-1314
species in Egypt and provide milk and milk products that are important sources of protein, energy, vitamins, and minerals for the diet of the Egyptian people. However, the amount of milk yield in Egypt is inadequate to meet the needs of the people there. A better understanding of factors influencing yield of buffalo is needed to increase the total amount of milk produced in Egypt. Animal health, feeding, and reproductive programs and their management account for 75% of variation in herd yield, and the remaining 25% is due to genetic sectors (3). The rate of secretion of milk in dairy animals displays a definite trend throughout the lactation period. Following parturition, daily milk yield increases to a peak and then gradually declines until the lactation is ended. Some lactations are terminated or truncated before the desired time (usually 305 d) because of low persistency (6). The shape of the lactation curve is influenced by parity and season of calving in cattle (25). Fann, parity, and season of calving influenced the shape of lactation curve of Egyptian buffalo (16). Qualitative and quantitative differences in feeding and management are among the important causes of variation in milk yield (18) and greatly influence the shape of the lactation curve. The shapes of lactation curves could be measured by the persistency of yield [i.e., the ratio of yields in consecutive periods (4)]. Maymone and Malossini (11) estimated the persistency of milk yield in buffalo as the ratio of amount of milk produced in the second 100 d of lactation to that produced in the first 100 d of lactation. Most studies of milk yield of buffalo have used only lactations of ~305 d (1, 17), but some have used lactations >150 d (16). The objectives of this study were to investigate the effects of herd-year-season and age at calving on the shape of the production curve
1306
1307
LACTATION CURVES
of first lactation buffalo and their persistency in lactations of different lengths. MATERIALS AND METHODS
Daily milk yield records were available from 1538 first lactation buffalo calving from 1967 to 1990 in herds at three experimental stations of the Animal Production Research Institute, (El-Nattaf EI-Gedid, EI-Nattaf EIKadem, and Mehallet Mousa, Egypt). The herds were maintained according to feeding and management standards adopted by the institute. During winter and spring (December to May), cows were grazed on Egyptian clover as the only source of feed. During summer and autumn (June to November), cows were kept under open sheds covered with asbestos roofs 4 m high. During this period, feeding consisted of a concentrate mixture, wheat or rice straw, and a limited amount of clover hay when available. The cows were milked by hand twice daily at 0730 and 1630 h without the presence of the calf. In order to include all possible variations in the shape of lactation curve, records were included whether or not 308 d of lactation were completed. Preparatory to this study, the daily milk yields were summed by l4-d intervals for the duration of the lactation. A total of 498 of the 1538 records had <29 d of lactation and were deleted from some analyses because of problems occurring before, at, or just after parturition. The remaining records were then sorted into four groupings: 1040 lactations >28 d, 344 lactations >28 and <150 d, 651 lactations >149 d, and 260 lactations ~308 d (22 periods) (Table I). The subsets were for estimation of
persistency of lactations of variable length >28 d, intennediate length> 149 d, and those ~308 d. Lactations >28 d included those >149 d, and those >149 d included those ~308 d. All records were used to detennine the pooled lactation curve with the following model using software of SAS (19). Yijklm
Record length (d)
(n)
>28 >28 and <:150 1 >149
1040 344 651
~308
260
Total
1538
(kg)
892 360 1229 1661 606
[1]
where Yijklm {30
HYSi bl ~
b3 Pj Pk PI eijklm
= 14-d milk yield = intercept, = random effect
record,
of herd-yearseason i, = partial linear regression of milk yield on stage of lactation (period), = partial quadratic regression of milk yield on (stage)2, = partial cubic re¥ression of milk yield on (stage) , = stage of lactation j (j = I, 2, 3... ,22), = (stage)2, = (stage)3, and = a random residual, normally and independently distributed with · 2 zero mean and vanance (Je'
The records of the three groups based on lactation length (>28 d but <150 d, >149 d, and ~308 d) were used to detennine the lactation curves. The three subsets were analyzed as follows.
= {30
+ HYSi + b 1(Gj x Pk) + b2(Gj x + b3(Gj x P~) + eijklmn
Lactation length (d)
+ HYSi + bl(Pj) + b2(P~)
+ b3(P~) + ~jklm
TABLE I. Mean milk yield and lactation length in the three different groupings and all records. Mean milk yield
= (30
ph
[2]
where
212
88 290 393 144
Yijklmn (Gj x Pk)
= 14-d milk yield record, = stage of lactation k (k = 1,2,...22) within group j (j = 1,2,3),
lThe group included to draw a separate curve. Journal of Dairy Science Vol. 77, No.5, 1994
1308
METRY ET AL.
(OJ x P~)
= (stageY
(OJ x P~)
= (stage)3
within group,
A2
within group,
A3
k I
and other descriptions are as in Model [I]. To determine the lactation curves by season of calving from all records, the following model was used. Yijklmn
= 130
+ HYj + bl(Sj x Pk) + b2(Sj x + b3(Sj x P~) + eijklmn [3]
ph
= (ageY. = (age>3,
and other descriptions are as in Model [I]. The effect of age at calving on milk yield by stage of lactation by season was calculated from the following model. Yijldmn
= f30 + HYi + Sj + bl(~) + b2(Ah + b3(A~) + b4(Sj x Ak)
+ bs(Sj x Ar) + b6(S x A3) + eijldmn [5]
where Yjjklmn HYj bl
= 14-d milk yield record, = random effect of herd-year i, = partial linear regression of
where 14-d milk record, season j of calving, partial linear regression of milk yield by stage on age at calving. b2 = partial quadratic regression of milk yield by stage on (ageY, b3 = partial cubic regression of milk yield by stage on (age)3, b4 = partial linear regression of milk yield by stage on age at calving by season, bs = partial quadratic regression of milk yield by stage on (ageY by season, b6 = partial cubic regression of milk yield on (age)3 by season, Ak = age k at calving in mo, = (ageY,
milk yield on stage within season, b2 = partial quadratic regression of milk yield on (stageY within season, b3 = partial cubic regression of milk yield on (stage)3 within season. (Sj x Pk) = stage of lactation k within season j of calving, [1 = spring (March to May), 2 = summer (June to August), 3 = autumn (September to November), and 4 = winter (December to February)], (Sj :-: = (stageY within season,
ph
(Sj x P 3) m
= (stage)3
within season, and
with f30 and eijldmn as described earlier. The effect of age at calving on milk yield for each stage of lactation (14 d milk yield) was obtained from the following model. Yijklm
= 130
+ HYS j + bl(Aj) + ~(A~)
+ b3(A?) + ~jklm
[4]
where Yijklm Aj
= 14-d milk record, at calving in G = 27,28,.... ,77),
= age j
months
Journal of Dairy Science Vol. 77, No. S. 1994
Ar
3 Am
= (age)3,
(Sj
x Ak) = age k at calving by season j, x Ah = (ageY by season.
(Sj
x A~)
(Sj
= (age>3
by season,
and other descriptions are as in Model [4]. Persistencies in all records and the three classes (>28, >149, and ~308 d of lactation) were each estimated as the ratio of milk yield in the second 100 d of lactation to milk yield in the fIrst 100 d of lactation (P2:1) (11) using Model [6],
1309
LACTAnON CURVES
Yijklmn =
t30 + HYi + Sj +
bl(~)
+ b2(Ar> + b3(A~) + b4(Sj x Ak)
+ bs(Sj x
At> + b6(S x
A3)
+ eijklmn
[6] Periods 2 in lactation
where Yijklm
TABLE 2. Regression of milk yield! by 14-d periods on age at calving, (age)2, (age)3, and percentage of variance due to age at calving within herd-year-season (HYS) for first lactation buffalo.
= the
persistency percentage,
and other descriptions are as in Models [4] and [5]. RESULTS AND DISCUSSION
The mean milk yield, lactation length, and numbers of records for the subsets and overall records are given in Table l. Of the total records, 32% were <29 d and were excluded from analyses because of problems before, at, and after parturition (abortion, stillbirth, or failed to lactate). Only 16.9% of the 1538 fIrst lactation buffalo completed lactations that were ~308 d in length. The mean milk yield was nearly doubled, from 892 kg for the 1040 records >28 d to 1661 kg for the 260 records ~308 d of lactation. Also, the mean lactation length increased from 212 to 393 d for the respective groups of records.
Age
(Age)2
(Age)3
12.9** 14.7** -9.7 -14.1 -3.9 -8.8 -10.7 -197 -10.2 -7.4 -10.9 -14.7 -13.8 -14.9 -16.9 -6.2 -18.5 1.0 -3.9 5.3 .8 6.8
-.28** -.33**
.002** .002** -.002 -.003 -.001 -.002 -.002 -.003 -.002 -.001 -.002 -.003 -.003 -.003 -.003 -.001 -.003 .001 -.001 .001
Variance due to age within HYS (%)
I
2 3 4 S 6 7 8 9 10 II 12 13 14 IS 16 17 18 19 20 21
22
.22 .36 .11
.23 .25
.46 .26 .18
.27 .36 .33 .36 .40 .13
.44 -.04 .08 -.12 -.03 -.15
.000
.001
.79 .38 .32 .53 .64
.66 .41 .76 .24 .56 .75 .48 .90 .61 .75 .52 .82 1.13 1.03 1.96 1.94 1.27
**p < .01. lAdjusted for HYS. 214-d Milk yield.
Effect of Age at Calving
Regressions of milk yield (adjusted for herd-year-season) from Model [4] by 14-d periods on age, (ageY, and (ageY at calving and percentage of variance because of age at calving within herd-year-season from Model [4] are in Table 2. The effects of age at calving, (ageY, and (age)3 were signifIcant (P < .01) for the first and second periods but not for periods 3 through 22. This result agrees somewhat with results of Singh and Yadav (20), who reported that mean milk yield by Murrah buffalo in India was not affected by age at fIrst calving. The percentage of variance because of age at calving within herd-year-season was small «1%) for early stages but increased to 1.27 by period 22 (Table 2). The effects of herd-year, season, and age at calving from Model [5J are shown in Table 3. Herd-year had a signifIcant effect (P < .01) on periods 1 through 16 (Table 3) but was not significant from periods 17 to 22. The herd-
year effect reflected the fluctuation in feed supply between years that was due to climatic conditions. These results are similar to those obtained in other studies of buffalo (16,20,24) and cattle (9, 22), but disagreed with observations by Khosla et al. (7), who reported that year of calving had no signifIcant effect on daily milk yield of first lactation buffalo in Pakistan. Their fIndings might have been influenced by the few years (1978 to 1980) covered by their study. Season of calving (Model [5]) was not significant for the 22 periods in milk. However, age at calving, (ageY, and (age)3 were significant (P < .01) in periods 1, 2, and 4 but not significant in periods 3 and 5 through 22 (Table 3). The percentage of variance because of periods within season was very small, .004, but was .11 for periods within herd-year. The Journal of Dairy Science Vol. 77, No.5, 1994
1310
METRY ET AL.
TABLE 3. Analysis of variance for factors affecting stage of lactation (14 d of lactation). Lactation periods l Source
df
Herd-year Season Age at calving (Age)2 (Age)3 (Age) x season (Age)2 x season (Age)3 x season
49 3 1 I 1 3 3 3
4
2
3
5.8** 1.1 3.3 t 2.91 2.4 1.1 1.1 1.0 18
3.3** 1.4 1.9 1.5 1.2 1.3 1.2 1.1 16
5 to 16
17 to 22
1.3 - 2.0** NS NS NS NS NS NS NS 14 - 18
NS NS NS NS NS NS NS NS IS - 23
F-value
R2, %
4.2** 1.1 8.8** 7.9** 7.0** 1.1 1.2 1.2 17
3.1** 1.3 2.7 3,P 3.6 t 1.3 1.3 1.3 16
1I4-d Milk yield,
tp < .10. *p < .05. "p < .01.
effects of age at calving, (ageY, and (ageY within season were not significant for all periods. Periods in milk were affected by factors other than season and age at calving, such as feeding, managerial practices, or the weather. Cockrill (4) reported that the effect of temperature and humidity were of great importance for milk yield in buffalo. Buffalo are more sensitive than cattle to heat exposure. As environmental temperatures rose, water consumption increased, but, if the feed intake was depressed, milk secretion decreased. Misra et al. (14) found that both food and water intakes in buffalo were reduced by ambient temperatures >32°C. Our findings agreed with those for Sahiwal cows of India (2) where season of calving had no significant effect on the weekly milk yield in the last few weeks of lactation. For Egyptian buffalo, Alim (1) and Salem (17) found that 305-d milk yield in multiple lactations of buffalo was not affected by season of calving. However, the results were not similar for Egyptian buffalo (5, 14) and for buffalo in Pakistan (7). Proportions of variance within the 22 periods attributable to the fifth analytical model ranged from R2 = .11 to .30 (fable 3). The contribution of herd-year to total variance within periods was 10 to 17%. These are less than the 30 to 38% of the total variance in milk yield by cattle in Brazil (12). The percentage of variance attributable to season of calving was relatively small at .54%. Journal of Dairy Science Vol. 77. No. S. 1994
lactation Curves
The estimates obtained from Model [1] were used to locate the points of the pooled curve (Figure 1). Estimates from Model [2] were used to obtain overall curves of expected yield for periods 1 through 12 for records >28 but <150 d and 22 for records >149 d and ~308 d (Figure 2). The pooled curve peaked at periods 7 and 8, decreased steadily until period 19, and then increased to period 22. The configuration of the lactation curve of records >28 but <150 d reached its peak at period I, main-
l00r--------------~
,...
80
20f-
4
6
8
10
12
14
16
18
20
22
p.,locta
Figure I, Overall lactation curve over 22 14-<1 periods for first lactation buffalo.
1311
LACTATION CURVES 100,-----------------,
100'1- - - - - - - - - - - i
80
:: -g
60
'iia. '6
:!..
40
:!!
E
20
20
\
~ I
oLI2
4
6
8
10
12
14
16
18
20
22
2
periods
_ 4
6
8
10
12
14
16
18
20
22
periods
Figure 2. Lactation curves over 22 14-d periods for flrstlactation buffalo with >28 d (0), >149 d (+), and ~308 d (.) of lactation.
Figure 3. Lactation curves over 22 14-d periods for seasons of calving spring summer (+). autumn (.), and winter (0) for first lactation buffalo.
tained this peak for three additional periods, and decreased rapidly until period 12, which reflected the low persistency. Records >149 d and ~308 d peaked at periods 5 and 6, respectively, and remained near the same level through periods 6 and 8 and then decreased until periods 21 and 22. The rate of decline in milk yield from the peak period to the next one was 5.0, 1.4, 1.3, and 1.5% for records >28 but <150 d, >149 d, >308 d of lactation, and all records, respectively. The mean rate of decline from the peak to period 12 was 22.1 % for records >28 but <150 d, but was only 3.1,2.8, and 1.3%, respectively, from peak to period 22 for records >149 d, ~308 d, and all records. Rates of decrease were less than reported for crossbred cattle in India (15). The rapid rate of decline in records >28 but <150 d and records >149 d was probably due to the short lactation records included, which terminated before 308 d of lactation. This result agrees with that of Singh et a1. (22), who reported that short lactations «305 d) were more common than long lactations (>305 d) for all parities of Murrah buffalo (956 short lactations out of 1609 records). Milk yield curves (Model [3]) for lactations initiated by calvings in the same season within herd-year are shown in Figure 3. The shape of the yield curve following winter calvings (December to February) was quite different from those of other seasons. The peak was similar to that for the other calving seasons. The ascend-
ing phase was seven periods; then yield declined rapidly from periods 8 to 19 and increased again from periods 20 to 22. Lactation rates following spring, summer, and autumn calvings remained at near peak levels for 2, 3, and 2 periods and declined steadily thereafter until periods 19, 21, and 22, respectively. The yield trend for winter calving was influenced between periods 8 and 19 by changes from winter feeding regimens (surplus energy and protein for milk yield from green clover, and mild weather) to summer feeding regimens (dry feed with high fiber and deficient protein, heat stress, and abrupt change from green to dry feed) and increased again at the beginning of the next winter season. This result agrees with reports that the differences in lactation curves of Flekvieh cattle in Hungary between calving seasons reflected differences in feeding (8). The trend following winter calvings agreed with that for imported Friesian cattle in Nigeria (23). Also, Madalena et al. (10) reported significant season effects on the parameters of the lactation curves of Holsteins in Brazil. Cows that calved in the wet season in Brazil had higher initial yield but were less persistent than those cows calving in the dry season.
e-).
Persistency
Persistencies (Model [6]) of milk yield as the ratio of the second 100 to the first 100 d of milk yield are presented in Table 4. The records with ~308 d of lactation had 102% Journal of Dairy Science Vol. 77. No. S. 1994
1312
METRY ET AL.
TABLE 4. Least squares means and standard errors for persistency! of first lactation buffalo calving in different seasons. Lactation records Items
>28 d
All records
X
SE
X
SE
X
SE
X
SE
.57 .62
.13 .03 .04 .03 .03
.85 .88 .89 .87
.11 .03 .03 .03 .02
1.02 1.01 1.11 1.06 .90
.10 .03 .04 .03 .03
.46 .52 .54 .41 .38
.10 .03 .03 .03 .03
Overall Spring Summer Autumn Winter 1A
>149 d
.64 .54 .48
.77
ratio of the second 100 and first 100 d of lactation.
persistency compared with persistencies of 85% in lactations >149 d, 57% in lactations >28 d, and only 46% in all records. A similarly calculated persistency of 83% was reported for first lactation buffalo in Italy (4). Records ~308 d of lactation had information in all periods, but records >28 d, >149 d, and all records had substantial numbers of records terminated earlier than 308 d of lactation. In addition, a higher proportion of the records in the >28 d, >149 d, and all records lactation groupings may have been influenced by poor design and management of health, nutrition, feeding, and reproduction programs. Also, lactations were terminated early because buffalo in poor condition at calving were unable to maintain acceptable milk yield. Mean persistencies for cows calving in spring, summer, autumn, and winter calvings
in records ~308 d of lactation were 10 I, Ill, 106, and 90%, respectively. Trends were similar for lactations >28 d, >149 d, and all records even though persistency was much lower. The similarity of trends indicates that the seasonality of production may be stimulated by the net effect of the season of year in which parturition occurred (16). The season stimulus is a consequence of nutrition, health, and climate and shows its influence at all stages of the lactation. Herd-year had a highly significant effect (P < .01) on persistency for all records, those >28 d, and those >149 d, and this effect was significant (P < .05) for the ~308-d grouping (Table 5). Season of calving affected (P < .05) the persistency of all records and of records >28 d (P < .01). Season was significant (P < .10) for records ~308 d but not for records
TABLE 5. Analysis of variance for persistencyl of lactation milk yield for records >28 d, >149 d,
df 49 3 1 1 1
984
>149 d
MS
df
1.15 u
.16 28.9
MS .18-.12
47 3
1.19-.30 .30 .27
4 4 4 588
.12 .12 .18* .07 222
!A ratio of the second 100 and first 100 d of lactation.
tp < .10. -p < .05. up < .01. Journal of Dairy Science Vol. 77. No.5, 1994
All records
MS
df
MS
28 3 1 1
.05.o7 t .16.17-
49 3
2.17-.39*
3 3
.06 .06
4
.30 t
220
.03 30.4
1481
.14 35.7
LACTATION CURVES
>149 d of lactation. These findings were similar to those of Zamorano Villarreal (26) with Friesian cows in Mexico. Age at calving had significant linear and quadratic effects (P < .05) on the persistency in ~308-d records but was not significant in >28-d records (Table 5), which agrees with findings (26) for cattle. This discrepancy could be explained by the wide variation in age at calving (27 to 77 mo) in the >28-d grouping; consequently, persistency varied. Correlation was positive but not significant between persistency and 308-d milk yield (r = .06), but negative between persistency and season of calving (r = -.11). However, the magnitude of correlation between persistency and milk yield was less than for first lactation Holstein-Friesians (r .35), which disagrees with Zamorano Villarreal (26).
=
CONCLUSIONS
Factors affecting the shape of lactation curves of buffalo are likely similar to those of cattle. A high percentage of the first lactation buffalo in this study had short lactations (37.4% had <150 d of lactation). Short lactations and the consequent low yearly milk yields drastically reduce the usefulness of buffalo as dairy animals. More research to identify the underlying genetic and environmental causes should be a high priority for areas where dairy buffalo are used. Seasonal differences suggest that improved management through adequate feeding for milk yield, disease prevention, parasite control, protection against extremes of climate, and a regular reproductive timetable could be useful to improve milk yield.
REFERENCES I Alim, K. A. 1978. The productive perfonnance of Egyptian buffalo in dairy herd. World Rev. Anim. Prod. 14:2. 2 Biswas, J. C., G. L. Koul, M. Kumar, P. N. Bhat, and G. Sing. 1986. Effect of non-genetic factors on weekly milk yield in Sahiwal cows. Indian 1. Anim. Sci. 56:1165. 3 Brackett, B. G., G. E. Seidel, Jr., and S. M. Seidel.
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1981. New Technologies in Animal Breeding. Academic Press, New York, NY. 4 Cockrill, W. R. 1974. The Husbandry and Health of the Domestic Buffalo. Food Agric. Organization U. N.• Rome, Italy. 5 EI-Irian. M. A. 1981. Studies on milk production of Egyptian buffaloes. M.Sc. Thesis, Fac. Agric., Univ. El-Mansourah, Mansourah, Egypt. 6 Gilmore, L. O. 1952. Environmental factors affecting production. Dairy Cattle Breeding. R. W. Gregory. ed. J. B. Lippincott Co., Philadelphia, PA. 7 Khosla, S. K., S. S. Gill, O. S. Pannar, and P. K. Malhotra. 1985. Factors affecting peak yield and yield per day of lactation in buffaloes under field conditions. 1. Res. Punjab Agric. Univ. 22:747. 8 Komarek, L., and A. Ruegsegger. 1986. Lactation curve for milk yield and milk composition. Simmentaler Fleclcvieh. 4: 14. 9 Lee, J. K., and B. K. Ohh. 1986. Importance and relative magnitude of environmental factors for milk yield in Korea dairy cattle. Korean J. Anim. Sci. 56: 1165. 10 Madalena, F. E., M. L. Martiz, and A. F. Freitas. 1979. Lactation curves of Holstein-Friesian and Holstein-Friesian x Gir cows. Anim. Prod. 29:101. II Maymone, B., and F. Malossini. 1961. Lactation curve in buffalo cows. Ann. 1st. Spero Zootec. Roma 8:3. 12 McDowell, R. E. 1983. Strategy for improving beef and dairy cattle in tropics. Cornell Int. Agric. Mimeo 1001. Cornell Univ., Ithaca, NY. 13 Misra, M. S., B. P. Sengupta, and A. Roy. Physiological reactions of buffalo cows maintained in two different housing conditions during summer months. Ind. 1. Dairy Sci. 16:203. 14 Mourad, K. A., E. A. Afifi, and L. H. Bedeir. 1990. Non-genetic factors influencing milk production traits in Egyptian buffaloes. Egypt. J. Anim. Prod. 27:1. 15 Patel, J. M., A. M. Patel, and A. D. Dave. 1989. First lactation trend in Jersey x Kankrej and Holstein x Kankrej FI crossbred. Indian J. Anim. Sci. 59:162. 16 Ragab, M. T., A. S. Abdel-Aziz, and A. Kamal. 1973. Effect of fann, parity and season of calving on the lactation curve in buffaloes. Egypt. 1. Anim. Prod. 13: 123. 17 Salem, A. Y. 1983. Effect of non-genetic factors on milk yield of buffaloes in Egypt. M.Sc. Thesis, Fac. Agric. Tanta Univ .• Kafr EI-Sheikh, Egypt. 18 Sandra. A. Q., M. A. Giannoni, A. A. Ramos, and H. Tonhati. 1987. Environmental effects on the variation of productive traits in Holstein-Friesian x Zebu crossbred cattle in the region of Sao Carlos, state of Sao Paulo, Brazil. I. Milk yield. Rev. Brasl. Genet. 5: 63. 19 SAS~ User's Guide: Statistics, Version 6.03 Edition. 1988. SAS Inst., Inc., Cary, NC. 20 Singh, C. V., and M. C. Yadav. 1987. Non-genetic factors affecting daily milk yield in Murrah buffaloes. Indian 1. Anim. Sci. 57 :56. 21 Singh, R. V., D. K. Sadana, and S. S. Tomar. 1988. Nature and distribution of the short and long lactations in buffaloes. Buffalo J. 4:85. 22 Thomas, P., S. Iype, E. Luiting, and H. Bakker. 1987. Journal of Dairy Science Vol. 77, No.5, 1994
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METRY ET AL.
Factors affecting first lactation milk yield in Brown Swiss crossbred cattle under field conditions in Kerala. Indian J. Anim. Sci. 57:331. 23 Udedibie. A.B.I.. I. Umo. and I. Shaibu. 1985. The Vomherd. II. Effect of lactation number and season of calving on lactational characteristics of imported Friesian cows. J. Anim. Prod. Res. 5:31. 24 Vij. P. K. 1986. Phenotypic and genetic parameters of
Journal of Dairy Science Vol. 77. No.5. 1994
some production traits in buffaloes. Indian Vet. J. 63: 838. 25 Wood. P.D.P.• 1969. Factors affecting the shape of the lactation curve in cattle. J. Anim. Prod. 11 :307. 26 Zamorano Villarreal. H. E. 1986. Quantitative analysis of lactation curve up to the 5th calving in commercial herd of Holstein-Friesian cows. Veterinaria (Mex. City) 17:133.