12. Growth and weight

Birthweight
Growth to maturity
Breeding female postpartum weights
Effects of climate on specific age and sex groups
Discussion

Birthweight

The observed birthweight ( ± s.d.) of 581 goats born in the years 1978 to 1984 was 2.2 (0.64 kg. The mean birthweight for 613 sheep during the same period was 2.9 ± 0.88 kg.

The analysis of variance of this trait for goats is shown in Table 41: sex, parity, type of birth and year of birth of the kid exerted significant effects on its birthweight. The least-squares means for kid birthweights are given in Table 42. This shows that, as might be expected, males were heavier than females at birth, young of older females weighed more than those from younger dams, and twins (and triplets) were lighter than kids born as singles. Although the year of birth had a significant effect on birthweight, the observed variation can not be clearly related to the rainfall pattern over the study period.

The analysis of variance for birthweight in sheep (Table 43) shows that basically the same sources of variation acted on this trait as in goats although in addition there were highly significant differences due to system. The least-squares means for lamb birthweights are given in Table 44. Lambs born in the irrigated rice subsystem were heavier than those from the rainfed millet subsystem, their dams presumably benefitting from the better nutritional conditions in that zone. The other sources of variation exerted effects similar to those for goats.

Growth to maturity

Generalised growth curves for goats and sheep from birth to maturity are given in Figure 45. Analyses of variance and estimated least-squares means for weights at various ages are shown in Tables 41 and 42 for goats and in Tables 43 and 44 for sheep. The observed sample means in Figure 45 differ from the least-squares means in Tables 42 and 44 as the data in the tables are adjusted for the unequal subclass numbers.

In goats, the system under which they were reared exerted a relatively minor effect (except at 150 and 240 days of age) until 1 year of age. The effects of parity were significant only up to 240 days and the effects of birth type, with the exception of some anomalous results around 2 years, were also quickly lost. Season of birth exerted a significant effect on weight only at 10 and 30 days. Sex had a consistently significant effect on weight as did year of birth. The effects of year of birth on growth to 3 years of age are shown in Figure 46. Kids born in 1981 exhibited a similar growth rate to those born in 1980, and kids born in all subsequent years again showed slower growth rates resulting in lighter weights-at-age when compared to kids born during 1978 and 1979.

In sheep, system had a highly significant effect on weight until mature weights were reached at about 3 years of age. The effects of the other sources of variation were similar to those observed for goats, with the exception of the effects of year of birth which were lost at about 1 year of age.

Average daily gains (calculated on the least-squares means) for goats from birth to 150, 365 and 1095 days were 58.0, 49.3 and 28.7 g/day respectively. In sheep, the average daily gains were 88.7, 66.9 and 33.3 g/day to the same ages. Asymptotic weights were achieved in sheep at about 3 years while goats were almost 4 years old before their growth curve leveled off.

Phenotypic correlations between weights at various ages up to 2 years are shown in Table 45. In general the correlations were better for sheep than for goats but all were highly significant for both species at all ages.

Table 41. Analysis of variance of weights-at-age for goats in central Mali.

Source of variation	Age (days)
	0		10		30	90	150		240		365		550		730		910		1095
	d.f.	MS	d.f.	MS	MS	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS
System	1	0.0	1	0.6	4.0*	14.5*	1	65.9**	1	168.5***	1	61*	1	37	1	35	1	20	1	3
Sex	1	3.0**	1	10.6***	17.9***	88.6***	1	208.7***	1	385.2***	1	609***	1	1 739*	1	1 882***	1	2 061***	1	1 446***
Parity	3	1.9***	3	13.1***	36.9***	49.9***	3	62.5***	3	28.0*	3	20	3	14	3	6	3	18	3	22
Type of birth	1	18.3***	1	67.2***	178.5***	170.5***	1	108.1***	1	29.2	1	0	1	129**	1	178***	1	68*	1	68
Season	3	0.0	3	2.4**	6.0***	3.2	3	4.6	3	10.7	3	44**	3	7	3	26	3	29	3	27
Year	6	1.9***	6	2.0***	3.0**	9.3*	5	13.1	5	26.7*	5	40**	4	108***	4	39*	3	103***	3	31
Season x System	3	0.0	3	1.0	2.6	1.1	3	4.5	3	2.3	3	3	3	5	3	9
Season x Sex	3	0.4	3	0.9	0.9	0.9	3	1.4	3	6.0	3	6	3	5	3	1	-	-	-	-
Season x Parity	9	0.2	9	0.4	1.2	2.4	9	3.9	9	7.8	9	16	9	9	9	13	-	-	-	-
Season x Birth type	3	0.6	3	1.2	1.6	14.8**	3	34.0**	3	22.0	3	4	3	12	3	12	-	-	-	-
Season x Year	16	0.5	16	2.2***	5.0***	12.9***	15	21.2***	13	41.9***	13	23*	12	19	10	16	-	-	-	-
Error	531	0.4	531	0.4	1.0	3.4	870	6.4	709	9.0	511	11	270	17	165	15	103	16	60	18

***P<0.001; **P<0.01; *P<0.05.

Table 42. Least-squares means of weights (kg) at specified ages for goats in central Mali.

Variable		0		10		30		90		150		240		365		550		730		910		1095
		n		n		n		n		n		n		n		n		n		n		n
Overall		581	2.20	1 054	3.03	1 215	4.32	1 066	7.7	918	10.9	755	15.2	557	20.2	314	25.2	207	29.8	116	33.3	73	33.6
System
Millet		514	2.21	860	3.00	967	4.25a	859	7.5a	743	10.6a	614	14.6a	478	19.7a	281	24.6	193	28.7	110	32.3	68	34.1
Rice		67	2.19	194	3.07	248	4.40b	207	7.9b	175	11.3b	141	15.9b	79	20.7b	33	25.8	14	30.9	6	34.2	5	33.2
Sex
	Female	290	2.12a	496	2.93a	576	4.20a	505	7.4a	431	10.4a	365	14.5a	309	19.1a	215	22.5a	154	25.8a	93	27.6a	61	27.0a
	Male	291	2.27b	558	3.14b	639	4.45b	561	8.0b	487	11.4b	390	16.0b	248	21.3b	99	27.9b	53	33.7b	23	38.9b	12	40.2b
Parity
	1	108	2.05a	187	2.68a	220	3.78a	183	6.9a	147	9.9a	116	14.5a	82	19.6	40	25.1	28	30.1	8	33.6	6	33.9
	2	83	2.12ab	165	2.99b	188	4.29b	163	7.8b	137	11.1b	118	15.5b	79	20.9	45	25.7	32	30.2	20	34.2	12	35.4
	3	82	2.30bc	140	3.20c	156	4.56	128	8.1b	110	11.5b	91	15.5b	71	20.2	37	25.2	23	29.4	10	32.9	7	31.3
	³ 4	308	2.32	562	3.26c	651	4.66c	592	8.0b	524	11.2b	430	15.5b	325	20.1	192	24.6	124	29.5	78	32.4	48	33.9
Type of birth
	Single	353	2.41a	665	3.33a	797	4.78a	705	8.2a	598	11.3a	488	15.5	355	20.2	191	24.4a	128	28.6a	65	32.4a	35	32.5
	Multiple	228	1.98b	389	2.73b	418	3.87b	361	7.2b	320	10.5b	267	15.0	202	20.2	123	26.0b	79	31.0b	51	34.1b	38	34.8
Season
	Cold dry	136	2.17	244	3.18a	287	4.51a	238	7.8	206	11.1	168	15.8	124	20.0ab	72	24.2	52	27.5	34	32.9	27	33.8
	Hot dry	175	2.23	296	2.87b	344	4.09b	310	7.8	270	11.2	229	15.0	159	18.8b	89	25.2	46	28.4	32	34.5	13	32.4
	Rains	113	2.21	191	3.22a	226	4.60a	207	7.8	187	10.6	152	14.8	125	20.8a	72	25.9	49	31.8	30	32.1	18	32.7
	Post-rains	157	2.19	223	2.86b	358	4.10b	311	7.4	255	10.8	206	15.4	149	20.2a	81	25.5	60	31.5	20	33.6	15	35.7
Year
	1978	67	2.12ab	67	3.32a	68	4.93a	62	8.0ab	57	10.9	48	15.7ab	40	20.2ab	17	27.8a	13	31.4a	12	35.3a	11	35.4
	1979	64	2.13ab	111	3.00bc	129	4.27b	123	8.2b	107	11.6	85	15.6ab	64	21.2a	40	27.0a	27	30.9a	16	35.1a	13	34.1
	1980	142	1.98a	257	2.87b	294	4.20b	257	7.5ac	229	10.6	189	14.5c	137	19.1b	94	23.9b	71	28.5b	51	31.0b	39	32.1
	1981	180	2.07ab	302	2.90b	322	4.25b	285	7.7ac	255	10.8	214	14.9bc	160	19.8ab	108	23.3b	85	28.3b	37	31.7b	10	33.0
	1982	72	2.19b	193	3.06ac	231	4.28b	210	7.6ac	193	10.7	163	14.8bc	123	19.7b	55	24.0b	11	29.9ab	-	-	-	-
	1983	42	2.69c	92	3.27a	124	4.34b	111	8.0ab	77	10.9	56	16.0a	33	21.1a	-	-	-	-	-	-	-	-
	1984	14	2.21ab	32	2.82bc	47	3.99b	18	6.9c	-	-	-	-	-	-	-	-	-	-	-	-	-	-

Within variable groups, means followed by different letters differ significantly (P<0.05). Variable groups without any letters did not show a significant difference in the analysis of variance.

Table 43. Analysis of variance of weights-at-age for sheep in central Mali.

Source of variation	Age (days)
	0		10		30	90	150		240		365		550		730		910		1095		1280		1460
	d.f.	MS	d.f.	MS	MS	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS	d.f.	MS
System	1	13.5***	1	132.4***	613.8***	3 113.5***	1	5 545***	1	6 138***	1	4 599***	1	2 011***	1	903***	1	3 378***	1	172**	1	54	1	12
Sex	1	2.7*	1	34.4***	133.7***	450.3***	1	998***	1	1 853***	1	3 408***	1	5 856***	1	3 319***	1	1 470***	1	1 067***	1	572***	1	399***
Parity	3	13.2***	3	34.2***	76.2***	144.0***	3	164***	3	71*	3	41	3	10	3	27	3	2	3	11	3	12	3	12
Type of birth	1	11.1***	1	73.6***	222.8***	308.0***	1	281***	1	169**	1	36	1	5	1	1	1	5	1	25	1	14	1	2
Season	3	1.4	3	2.6	16.9***	43.3**	3	35	3	23	3	26	3	18	3	18	3	18	3	29	3	29	3	16
Year	6	1.0	6	1.8	17.3***	58.5***	6	105***	5	84**	5	117***	5	46	4	39	4	5	3	15	3	11	2	37
Season x System	3	1.2	3	0.5	1.4	16.1	3	34	3	72*	3	41	3	10	3	46	3	15	3	36	-	-	-	-
Season x Sex	3	0.3	3	2.0	6.9	16.3	3	30	3	11	3	17	3	6	3	49	3	71	3	16	-	-	-	-
Season x Parity	9	1.3*	9	1.3	2.9	11.9	9	15	9	21	9	29	9	26	9	12	9	11	9	10	-	-	-	-
Season x Birth type	3	0.5	3	0.3	2.3	19.4	3	18	3	5	3	4	3	8	3	1	1	65	1	24	-	-	-	-
Season x Year	17	0.9	16	1.6	9.1***	39.0***	15	63***	15	66***	14	22	12	24	11	36	9	14	7	10	-	-	-	-
Error	562	0.6	a)	1.1	2.9	10.5	1 063	16	816	23	560	27	332	26	193	20	113	21	64	24	53	23	35	19

***P<0.001; **P<0.01; *<0.05.

Table 44. Least-squares means of weights (kg) at specified ages for sheep in central Mali.

Variable		0		10		30		90		150		240		365		550		730		910		1095		1280		1460
		n		n		n		n		n		n		n		n		n		n		n		n		n
Overall		613	2.79	1 113	3.87	1 333	5.98	1 238	11.8	1 112	16.1	864	21.5	607	27.2	377	32.0	236	35.1	152	36.0	100	39.2	66	37.2	47	37.9
System
	Millet	469	2.60a	763	3.47a	900	5.21a	821	10.0a	732	13.6a	563	18.5a	406	23.9a	268	29.0a	179	32.2a	124	33.5a	86	35.3a	58	35.1	43	36.7
	Rice	144	2.98b	350	4.27b	433	6.75b	417	13.6b	380	18.6b	301	24.5b	201	30.4b	109	34.9b	57	38.0b	28	38.5b	14	43.2b	8	39.2	4	39.1
Sex
	Female	307	2.72a	563	3.0a	684	5.65a	638	11.2a	587	15.1a	484	20.0a	384	24.6a	20	27.4a	192	29.7a	134	30.6a	87	33.1a	58	32.4a	40	33.5
	Male	306	2.86b	550	4.05b	649	6.31b	600	12.4b	525	17.1b	380	23.0b	223	29.8b	108	36.5b	44	40.4b	18	41.4b	13	45.3b	8	42.0b	7	42.3
Parity
	1	163	2.35a	253	3.36a	301	5.29a	274	10.7a	245	14.9a	187	20.5a	120	26.5	78	31.5	44	34.6	23	35.7	16	38.5	12	36.3	8	39.1
	2	118	2.85b	223	3.87b	261	5.94b	240	11.8b	224	16.3b	176	21.8b	126	26.8	82	31.8	54	34.3	37	36.0	23	38.6	10	37.3	7	35.6
	3	73	3.00b	159	4.09c	195	6.34c	188	12.4b	171	16.7b	129	22.1b	94	27.9	57	32.3	40	35.6	28	36.4	20	40.7	15	38.4	11	39.0
	³ 4	259	2.97b	478	4.16c	576	6.35c	536	12.2b	472	16.5b	372	21.6b	267	27.5	160	32.2	98	35.8	64	36.1	41	39.1	29	36.7	21	38.0
Type of birth
	Single	563	3.13a	1 015	4.47a	1 224	6.94a	1 145	13.0a	1 029	17.3a	798	22.6a	563	28.0	351	32.4	220	35.3	144	36.5	95	40.5	63	38.4	44	38.4
	Twin	50	2.45b	98	3.27b	109	5.03b	93	10.6b	83	14.9b	66	20.4b	44	26.4	26	31.5	16	34.8	8	35.6	5	38.3	3	35.9	3	37.5
Season
	Cold dry	147	2.88	306	3.88	372	6.11b	331	11.9ab	297	15.8	211	22.6	156	27.2	103	30.6	59	36.8	41	38.4	18	41.2	17	35.2	7	39.7
	Hot dry	160	2.50	301	3.66	351	5.61a	316	11.4a	294	16.4	232	21.1	175	26.3	102	32.2	72	34.7	42	34.7	20	34.9	19	37.7	16	36.6
	Rains	158	3.02	275	4.24	320	6.79b	323	13.2b	278	17.3	224	21.4	159	29.1	94	33.6	57	36.6	37	35.1	33	41.2	15	39.1	11	36.9
	Post-rain	148	2.76	231	3.70	290	5.42a	268	10.7a	243	14.9	197	20.9	117	26.1	78	31.4	48	32.2	32	35.9	29	39.6	15	36.7	13	38.3
Year
	1978	102	3.07	124	4.18	135	6.86a	129	13.0a	111	17.9a	83	22.9a	65	28.7a	38	32.4	30	37.2	21	36.3	17	39.7	13	38.5	8	40.6
	1979	68	2.0	106	3.97	126	6.05ab	121	12.5ab	120	17.2ab	108	22.5ab	85	27.5ab	62	32.0	44	35.1	36	37.0	33	40.7	28	36.8	25	37.3
	1980	107	2.79	203	3.83	245	5.80ab	239	11.3bcd	205	15.6bc	166	20.9ab	122	26.3ab	75	32.0	56	34.8	44	35.7	29	38.2	20	36.3	14	35.9
	1981	111	2.69	221	3.78	249	5.94ab	229	12.2ac	218	16.6ab	175	21.4ab	135	27.0ab	97	31.2	71	34.7	47	36.2	21	38.3	5	37.1	-	-
	1982	91	2.65	196	3.86	234	6.08ab	220	11.8acd	208	15.8bc	174	20.6b	130	25.2b	58	30.3	35	33.5	4	35.0	-	-	-	-	-	-
	1983	94	2.79	190	3.85	251	5.90ab	238	11.4acd	212	15.7b	158	20.7ab	70	28.5a	17	33.9	-	-	-	-	-	-	-	-	-	-
	1984	40	2.86	73	3.62	93	5.25b	62	10.3d	38	13.9c	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-

Within variable groups, means followed by different letters differ significantly (P<0.05). Variable groups without any letters did not show a significant difference in the analysis of variance.

Figure 45. Generalised growth curves from birth to maturity for goats and sheep in central Mali.

Figure 46. Relationship between year of birth and subsequent growth to 3 years of age in central Malian goats.

Breeding female postpartum weights

The observed means ( ± s.d.) for this character were 26.0 ± 5.16 (n = 1729) for goats and 30.0 ± 5.33 (n = 1536) for sheep.

The mean squares from the analysis of variance are set out in Table 46. The weight of goats was significantly affected by the system in which they were reared, the parity (age) of the animal, the type of parturition and the season and year during which the doe gave birth. The effects of flocks within systems were also highly significant. There were also significant effects due to the interactions of season with the system, with parity, parturition type and year. In sheep, postpartum weight was affected by the same sources of variation except season and year of parturition, and, of the interactions, only that of season x system was significant.

The estimated least-squares means for postpartum weights are given in Table 47 and graphic representations of the main variables affecting them are shown in Figure 47. Weights were higher for both goats and sheep in the irrigated rice subsystem than in the rainfed millet subsystem, and in both species females that had given birth to twins (or triplets) were heavier than those that had given birth to singles. Primiparous females in both species were lighter than multiparous ones, the progression being linear from first to fourth and greater parities. Goats at first kidding (82.2% of the overall mean) were relatively lighter than sheep at first lambing (87.9% of the overall mean) but both species achieved the overall mean weight by the time of second parturition.

Table 45. Phenotypic correlations between weights at various ages for goats and sheep in central Mali.

Age (days)		Age (days)
		30	90	150	240	365	550	730
Goats
	10	0.89	0.67	0.56	0.45	0.33	0.32	0.36
	30		0.73	0.62	0.49	0.38	0.42	0.40
	90			0.84	0.70	0.52	0.62	0.55
	150				0.79	0.52	0.62	0.55
	240					0.67	0.56	0.58
	365						0.62	0.73
	550							0.72
Sheep
	10	0.84	0.65	0.61	0.68	0.64	0.52	0.55
	30		0.82	0.78	0.74	0.70	0.64	0.66
	90			0.88	0.77	0.69	0.70	0.61
	150				0.79	0.63	0.62	0.53
	240					0.83	0.75	0.68
	365						0.80	0.74
	550							0.77

Table 46. Analysis of variance of postpartum weights of goats and sheep in central Mali.

Source of variation	Goats		Sheep
	d.f.	MS	d.f.	MS
System	1	755.9***	1	1 350.3***
Sex	1	0.5	1	55.6
Parity	3	5 257.3***	3	2 852.8
Type of parturition	1	154.3***	1	179.6***
Season	3	58.8**	3	22.0
Year	6	43.6***	6	5.7
Flock/millet	13	312.6***	14	411.2
Flock/rice	5	177.4***	16	170.5
Season x System	3	87.8***	3	60.4
Season x Sex	3	5.0	3	20.9
Season x Parity	9	22.0*	9	18.2
Season x Type of parturition	3	40.2*	3	20.9
Season x Year	16	23.0*	16	15.8
Error	1 661	11.5	1 456	15.9

***P<0.001; **P<0.01; *P<0.05.

The effects of season were rather different on the different species, goats being lightest in the cold dry season and then gaining weight in the hot dry season while sheep were lightest after a parturition during the hot dry season. The effects of year, although not significant in sheep, had similar trends in both species but the overall changes over the period of study were not marked.

Effects of climate on specific age and sex groups

Seasonal weight changes of selected age and sex groups of both species in both subsystems observed in relation to the overall mean weight-for-age are shown in Figure 48. Maximum and minimum weights in relation to the overall mean for all age and sex groups are given in Table 48. The magnitude of the seasonal effects was much less than that on cattle (as might also be inferred from a comparison of Tables 23 and 24 with Tables 41 to 44). There were no major response differences due to seasonal effects between subsystems or between species.

In general, minimum weights were observed for each sex, age class and species of stock in the millet subsystem in June and maximum weights in the post-rains period in October and November, although there was more variation in the timing of maximum weight than there was in the timing of least weight.

Table 47. Least-squares means for postpartum weights (kg) of goats and sheep in central Mali.

Variable		Goats			Sheep
		n		SE	n		SE
Overall		1 729	25.8	0.18	1 536	31.5	0.35
System
	Millet	1 348	24.7a	0.17	1 059	29.8a	0.37
	Rice	381	26.9b	0.27	477	33.1b	0.42
Sex
	Female	809	25.8	0.20	770	31.3	0.38
	Male	920	25.8	0.19	766	31.7	0.36
Parity
	1	422	21.2a	0.24	381	27.7a	0.40
	2	291	25.3b	0.27	293	31.5b	0.42
	3	207	27.2c	0.28	218	32.8c	0.43
	³ 4	809	29.4d	0.18	644	33.9d	0.36
Type of parturition
	Single	1 406	25.3a	0.17	1 468	30.4a	0.19
	Multiple	323	26.2b	0.25	68	32.5b	0.65
Season
	Cold dry	435	24.9a	0.29	436	31.0	0.51
	Hot dry	448	25.7a	0.36	415	30.9	0.43
	Rains	311	26.8b	0.29	357	32.9	0.94
	Post-rains	535	25.6a	0.36	328	31.1	0.69
Year
	1978	108	24.8d	0.49	153	31.4	0.54
	1979	150	26.4bcd	0.35	161	31.8	0.47
	1980	389	26.5b	0.22	293	31.5	0.41
	1982	308	25.9ac	0.24	262	31.5	0.44
	1983	307	25.6ad	0.26	274	31.3	0.43
	1984	126	25.3ad	0.36	115	31.4	0.54
Flock/millet
	Best	100	27.8	0.37	97	33.6	0.53
	Worst	37	20.7	0.58	67	23.8	0.61
Flock/rice
	Best	36	29.7	0.58	4	42.8	2.06
	Worst	72	24.6	0.43	14	27.8	1.13

Within variable groups, means followed on different letters differ significantly (P<0.05). Variable groups without any letters did not show a significant difference in the analysis of variance.

In the rice subsystem there was slightly more variability in the timing of both the minimum and maximum weights. As in the millet subsystem, female goats attained maximum weights in the post-rains period, but sheep tended to be heaviest in the late cold dry and early hot dry periods, this probably being related to the availability of weedy regrowth in the harvested rice fields at that time.

Resulting in large part from the low effects of season on weight, the growth curves of goats and sheep do not exhibit the same marked type of saw-tooth pattern as that observed in cattle. Examples of actual growth curves for female sheep in the millet subsystem are given in Figure 49.

Long-term weight changes over the study period are shown in Figure 50 for mature female sheep and goats in both subsystems. Table 49 provides information on the regression coefficients of these long-term weight changes. Although, as with cattle, the general trend in mature weight has been downwards, the monthly and total losses have been much less spectacular. Animals in the rice subsystem suffered less than those in the millet subsystem, sheep weighing 5.1% less at the end of 1983 than they did at the beginning of 1978 while in the millet subsystem sheep weighed 5.8% less. Goats in the rice subsystem actually weighed 2.5% more at the end of the study than at the beginning, but goats in the millet subsystem suffered most of all and were 9.9% lighter the end of 1983 compared with the beginning of 1978.

Figure 47. Relationships between postpartum weights and parity, season and year of birth of small ruminants in central Mali.

Discussion

The growth rates observed during this study were within the range reported for other African goats and sheep of similar mature size and are not indicative of any serious nutritional constraints when compared to the growth rates of cattle in the same environment. The gain in goats to 1 year after weaning was at 85% of the preweaning gain and in sheep at 75% these figures compare with a postweaning gain in cattle of only 65% of the preweaning gain. The effects of season on postweaning gain were not significant in sheep and, although significant in goats between 8 months and 1 year of age, these were not marked.

The effects of year were generally significant on weights-at-age and these can in general terms be related to the decline in rainfall and the reduced availability of total feed resources. The lighter weights at relatively mature ages (2 and 3 years) of animals born later in the study are what would be expected from the decline in weight noted for specific ages and sexes of animals in Figure 50 and Table 49. The inflection point in the growth curve occurred generally at about 12 months of age but was less marked for goats than for sheep.

Postpartum weights followed the pattern that could be expected in relation to the age of the dam. Postpartum weights in relation to the season of birth differed in pattern between goats and sheep. While maximum postpartum weights were observed in both species after a birth in the rainy season, lowest weights were noted for goats during the cold dry season and for sheep during the hot dry season. Goats presumably benefitted nutritionally from leaf development by some browse species as humidity increased during March and April. Postpartum weights as affected by season did not show the same trend as for cattle. For both goats and sheep they remained fairly constant about the mean over the 6-year study period.

The relative lack of seasonal effects on growth was also reflected in the intra-annual weight changes in specific age and sex groups for both goats and sheep. Although some weight losses occurred in all age groups due to seasonal effects (Table 48 and Figure 48), these were much less than in cattle. In general terms weights did not deviate from the mean by more than 6% in either direction for each species, sex and age group and in both subsystems. This should be compared with deviations of about 15% for female cattle and up to or more than 20% for work oxen. In practice, the effects of being reared in the rice subsystem appeared to be to delay the loss of weight in the cold dry season but there was a much less marked increase in growth rate in goats and sheep than in cattle in this subsystem due to the availability of weed growth after the rice harvest (March-April). Resulting from the less severe seasonal effects, growth to maturity proceeded with less fluctuations for goats and sheep than for cattle (Figures 48 and 35 respectively), and this applied to whatever season of year that young were born.

The long-term decline in mature weight was also much less serious in goats and sheep (Figure 50) than in cattle (Figure 36). Losses on a comparative basis were in general less than half those suffered by cattle. Both species lost less weight in the rice than in the millet subsystem.

Seasonal variations in weight of corresponding age and sex groups of small ruminants in central Mali.

Sheep

Goat

The better adaptation of both goats and sheep to the harsh conditions of the semi-arid environment and to the generally fluctuating feed supply are clearly evident in these observations on weight. The results also show that in the medium term, the forage supply has deteriorated in comparative terms more drastically for cattle than for small ruminants.

Table 48. Weight changes by sex and age in central Malian goats and sheep, expressed as percentages of mean annual weight.

Species, sex and agea			Millet subsystem				Rice subsystem
			nb	xc	Weight change (%)		nb	xc	Weight change (%)
					min	max			min	max
Goats
	Males:	1	642	25.1	93.0	106.5	167	24.7	91.1	10.7.9
		2	380	30.3	95.6	104.6	51	30.4	93.5	108.3
		3	309	34.7	87.6	110.5	49	29.8	94.1	104.9
		4	385	40.9	96.8	104.9	14	30.8	90.9	107.1
	Females:	1	1 342	20.4	91.8	105.0	218	20.9	94.1	109.3
		2	1 026	22.5	91.9	106.3	145	23.3	95.4	109.2
		3	1 300	24.9	96.2	103.1	179	26.0	96.7	105.4
		4	4 257	28.0	94.0	104.3	789	28.8	97.5	107.8
Sheep
	Males:	1	574	34.8	92.5	105.7	199	40.7	89.6	104.7
		2	221	37.7	96.6	107.3	62	45.1	91.2	113.2
		3	147	43.8	92.4	110.5	10	51.2	95.7	111.1
		4	442	45.9	96.4	104.4	-	-	-	-
	Females:	1	1 159	25.7	91.7	105.3	566	29.6	94.6	102.6
		2	908	27.8	96.2	107.1	428	31.4	96.1	104.1
		3	1 090	29.7	94.0	103.8	461	33.1	94.5	104.0
		4	3 088	31.2	94.2	104.4	835	33.1	93.0	104.9

^a Age given as pairs of permanent incisors.
^b Number of observations in each class of stock.
^c Mean annual weight in kg.

Figure 49. Long-term growth patterns for female sheep born in the millet subsystem in May to June and in October to November each year from 1978 to 1982.

Long-term variations in weight of sheep and goats in the rice and millet subsystems of central Mali.

Sheep

Goats

Table 49. Regressions of weight (kg) on time^a for mature female sheep and goats and of rainfall (mm) on time, central Mali.

Subsystem/species		Number of observations	a	b	r	P
Rice
	Sheep	657	-0.024	33.6	-0.0896	0.0216
	Goats	789	0.010	28.4	0.0331	0.3533
Millet
	Sheep	1 727b	-0.026	32.1	-0.1117	0.0000
	Goats	1 727b	-0.041	29.8	-0.1714	0.0000
Rainfallc		7	-33.4	452.1	-0.7871	0.0450

^a Monthly change; intercept at December 1979.
^b Random sample selected from 3 088 observations for sheep and 4 257 observations for goats.
^c Intercept at January 1977 and values for years not months.