Tracing sheep binary C3–C4 diet using stable isotope ratio (δ¹³C)

Figures & data

Table 1. Chemical composition of diets as fed, with legume sabiá (Mimosa caesalpiniifolia Benth.) in different inclusion levels in signalgrass hay.

Variable (g kg^–1)	Inclusion level of sabiá in signalgrass hay (brachiaria:sabiá)
	100:0	75:25	50:50	25:75	0:100
DM	822	806	814	818	828
OM	918	922	914	908	897
MM	82	78	86	92	103
CP	34	58	42	118	148
EE	14	23	32	38	46
NDF	695	663	608	584	549
NSC	174	178	231	167	153
TC	869	841	840	751	702

DM: dry matter; OM: organic matter; MM: mineral matter; CP: crude protein; EE: ether extract; NDF: neutral detergent fiber; NSC: non-structural carbohydrates; TC: total carbohydrates.

Table 2. Dry matter, organic matter, nutrient intake, faecal production, body weight, and DM digestibility of sheep fed signalgrass hay with various inclusion levels of legume sabiá (Mimosa caesalpiniifolia Benth.) hay.

Variable	Inclusion level of sabiá in brachiaria hay (brachiaria:sabiá)					p		SE
	100:0	75:25	50:50	25:75	0:100	L	Q
DMI (g DM d^-1)	352.7	384.9	382.5	399.3	429.7	0.1417	0.9061	34.8
OMI (g DM d^-1)	323.9	356.0	350.3	363.2	384.3	0.2209	0.9786	32.0
MMI (g DM d^-1)	28.7	28.9	32.2	36.1	45.4	0.0006	0.1277	3.2
CPI (g DM d^-1)	12.2	18.4	14.9	47.3	61.9	<0.0001	0.0020	4.0
EEI (g DM d^-1)	5.4	9.7	12.8	15.6	20.3	<0.0001	0.8512	1.3
NDFI (g DM d^-1)	261.1	269.7	243.6	250.2	250.5	0.5833	0.8521	23.0
NSCI (g DM d^-1)	45.2	58.7	79.0	50.0	51.6	0.8864	0.0400	8.9
TCI (g DM d^-1)	306.4	328.3	322.6	300.2	302.1	0.6895	0.6000	28.5
TFP (g DM d^-1)	234.0	283.5	303.8	321.0	245.4	0.2659	0.0006	17.6
BW (kg)	16.8	17.2	17.5	17.2	16.2	0.1848	0.0046	0.6
DDM (g DM kg^-1)	399	254	324	223	422	0.9256	0.0200	52
Signalgrass intake (%DM)	100	73	48	25	0	–	–	–
Sabiá intake (%DM)	0	27	52	75	100	–	–	–

DMI: dry matter intake; OMI: organic matter intake; MMI: mineral matter intake; CPI: crude protein intake; NDFI: neutral detergent fibre intake; NSCI: non-structural carbohydrate intake; TCI: total carbohydrate intake; TFP: total faecal production; BW: body weight; DDM: digestible dry matter.

Table 3. Dietary and faecal δ¹³C at different inclusion levels of legume sabiá (Mimosa caesalpiniifolia Benth.) and signalgrass hay.

Brachiaria hay: Sabia hay ratio	Diet (as fed) δ^13C (‰)	Faeces δ^13C (‰)	p^a
100:0	–17.84 ± 0.39	–18.37 ± 0.41	.13
75:25	–21.47 ± 1.19	–22.55 ± 0.61	.12
50:50	–25.56 ± 1.36	–27.51 ± 1.62	.03
25:75	–29.95 ± 0.55	–29.94 ± 0.43	.97
0:100	–33.89 ± 0.50	–33.74 ± 0.30	.57

^aProbability of difference comparing diet and faecal samples suing T-distribution test.

Figure 1. Proportion of C4 plants in the diet, predicted by different models. Equation 1: %C4 = 100- {100*[(δ¹³C faeces - δ¹³C; C4 plant)/ (δ¹³C; C3 plant - δ¹³C; C4 plant)]}; Equation 2: %C4 = 100-{100*[(δ¹³C faeces - δ¹³C; C4 plant-Δδ)/(δ¹³C; C3 plant - δ¹³C; C4 plant)]}; Eq 3a: %C4 = 100-100/ ({[Indigestibility C3*((δ¹³C; C3 plant + Δδ)- δ¹³C faeces)]/[Indigestibility C4*(δ¹³C faeces -(δ¹³C; C4 plant +Δδ)))]} + 1); Equation 3b: %C4 = 100-100/({[Digestibility C3*((δ¹³C; C3 plant + Δδ)- δ¹³C faeces)]/[Digestibility C4*(δ13C faeces -( δ¹³C; C4 plant +Δδ)))]} + 1); Equation 4: %C4 = 100- {100*[(δ¹³C faeces - δ¹³C faeces; C3)/(δ¹³C faeces; C4- δ¹³C faeces; C3)]}.