Will work on Macs if people have Office for Mac

. However I would agree a universal format would be better. Are you aiming for people to complete the document electronically or to print and fill in by hand and scan/post back? I presume the former as there is no return address, in which case you could look at something like Survey Monkey - you could have 2x 10 question questionnaires and up to 100 responses to each for free.
Hope I'm not teaching you to suck eggs, but from experience of surveys and data gathering to get good response rates people need to know a little bit about why it is being done and what will happen with their answers - is there anything in it for them or any risks for them? Will they get to see the final report or aggregated responses if they would like to?
The questions themselves need to be very clear and not leave room for interpretation, otherwise you will get lots of different interpretations which weakens your data. So, thoughts:
In general be clear which questions are "best single answer" and which are "tick all that apply". What is obvious to one person won't be to another.
1a. As mentioned there are more regions. But does everyone agree whether their county is in the midlands or the north, for example? You could have a free-text box for county name (or a drop-down list of all counties if doing online completion) that would remove this issue. You can allocate to regions in your analysis if desired.
1b. Is flock size all animals or only females or only females of breeding age? Does it include the lambs and if so what time of year are you measuring it?
The 500-1000 has a typo (is 5-1000 at the moment) and the ranges overlap, so e.g. 500-1000 / 1000-1500 should be 500-999 and 1000-1499. I presume you have chosen the bands as they make sense in the context you are analysing things and are broken down enough.
1c. Do all farmers agree on what group their breed fits in to? Is the group breed-specific or determined by location? For example would a Herdwick farmer in Cumbria tick the same box as a smallholder with Herdwicks on lower ground?
1d. The product could also be live animals e.g. to sell to other smallholders or to other farms lower down.
1f. How closed is closed? Completely, or are tups allowed in when needed?
2a. Nowhere to prompt people where to write the period. Perhaps split into two questions, first asking which month lambing begins in and the second for how many weeks they aim for it to run over?
2c. Options are too subjective - perhaps every time / every 2-5 / every 6-10 / more than every 10 / never?
2d. Percentages at scanning and lambing will be different - which one do you want to measure? Are you only counting live births?
2f. Is predation common enough to include as an option?
2h. If you want to draw any relationships between the answer here and other things like mortality you might need to know what proportions they are in.
3. Do you need to have sheep as an option? They won't have got this far unless they have them

What about poultry, goats?
Apologies if some of the above sounds nonsense as that will be due to me not understanding the subject fully, but I hope some of it is useful and helps you get really good data for your project. I'm presuming you've worked out your analysis plan already and the questions you are hoping to use this data to answer and have made sure that it will enable you to do that.