How to use the sheep gestation chart
Each block is one breeding month. Find the day the ewe was bred in the left column. The date in the right column is when she should lamb, 147 days later. A line marks where the lambing dates move into a new month.
For one ewe at a time, with her scanning, CDT booster and lambing-jug dates, use the sheep gestation calculator. It also turns the ram's in and out dates into a lambing calendar by 17-day heat cycle.
Why 147 days
Montana State Extension puts sheep gestation at 147 days on average, with breeds ranging from 144 to 151. Purdue Extension gives 148. Ewes of the same breed can differ by 3 to 5 days, so the chart's typical range runs 5 days either side of the date.
- Finn and early-maturing meat breeds: about 144 to 145 days (the chart uses 145).
- Rambouillet and other fine-wool breeds: about 150 to 151 days (the chart uses 150).
- Most other breeds and crossbreds: 147 days.
A ewe cycles about every 17 days. Montana State notes that a 35-day breeding season gives each ewe two chances to settle, and 60 days gives her three. Look up your ram-in and ram-out days on the chart to see how long lambing will run.
Printing the chart
"Print this" prints only the chart: the first six months on page one and the last six on page two. It fits Letter or A4 paper.
Leap years are handled. February 29 shows up only in a leap year, such as 2028, and every date is counted in whole days. A ewe bred on October 15, 2027 is due Fri, Mar 10, 2028, a day earlier on the calendar than a ewe bred the year before, because February 29, 2028 falls inside her pregnancy.